Optical-based validation of orientations of internal facets

ABSTRACT

Disclosed herein is a method including: providing a light guiding arrangement (LGA) configured to redirect light, incident thereon in a direction perpendicular to an external surface of the sample, into or onto the sample, such that light impinges on an internal facet of the sample nominally normally thereto; generating a first incident light beam (LB), directed at the external surface normally thereto, and a second incident LB, parallel to the first incident LB and directed at the LGA; obtaining a first returned LB by reflection of the first incident LB off the external surface, and a second returned LB by redirection by the LGA of the second incident LB into or onto the sample, reflection thereof off the internal facet, and inverse redirection by the LGA; measuring an angular deviation between the returned LBs and deducing therefrom an actual inclination angle of the internal facet relative to the external surface.

TECHNICAL FIELD

The present disclosure relates generally to methods and systems formetrology of samples including internal facets.

BACKGROUND

Some transparent optical elements, such as glass prisms and waveguides,may include reflective, internal facets. In order to validate to highprecision the orientation of such a facet relative to one or moreexternal surfaces of the optical element, current state-of-the-arttechniques require high-end optical components and implementation ofcomplex alignment and calibration procedures. There is thus an unmetneed in the art for simple and easily implementable metrologytechniques, which avoid the use of high-end optical components, therebyaddressing mass production demands.

SUMMARY

Aspects of the disclosure, according to some embodiments thereof, relateto methods and systems for metrology of samples including one or moreinternal facets. More specifically, but not exclusively, aspects of thedisclosure, according to some embodiments thereof, relate tooptical-based methods and systems for metrology of samples including oneor more internal facets.

Advantageously, the present application discloses fast, simple, andprecise methods and systems for validating the inclination of aninternal facet of a sample, or a plurality of nominally parallelinternal facets of a sample, relative to one or more external, flatsurfaces of the sample.

Thus, according to an aspect of some embodiments, there is provided anoptical-based method for validating an orientation of one or moreinternal facets of a sample relative to an external, flat surfacethereof. The method includes:

-   -   Providing a sample including an external, flat first surface and        an internal facet nominally inclined (intended by design and        fabrication to be inclined) at a nominal inclination angle μ        relative to the first surface.    -   Providing a light guiding arrangement (LGA) configured to        redirect light, which is incident on the LGA in a direction        perpendicular to the first surface, into or onto the sample,        such that light, transmitted thereby into the sample, impinges        on the internal facet nominally normally to the internal facet.    -   Generating a first incident light beam (LB), directed at the        first surface normally thereto, and a second incident LB,        parallel to the first incident LB and directed at the LGA.    -   Obtaining a first returned LB by reflection of the first        incident LB off the first surface.    -   Obtaining a second returned LB by redirection by the LGA of the        second incident LB into or onto the sample, reflection thereof        off the internal facet, and inverse redirection by the LGA.    -   Measuring a first angular deviation of the second returned LB        relative to the first returned LB.    -   Deducing an actual inclination angle of the internal facet        relative to the first surface, based at least on the measured        first angular deviation.

According to some embodiments of the method, the sample includes a firstpart and a second part, between which the internal facet extends. Thefirst part is positioned between an external second surface of thesample and the internal facet. A transmitted LB, which constituting aportion of the second incident LB, is directly or indirectly transmittedinto the sample, and enters into the sample via the second surface.

According to some embodiments of the method, the LGA includes a lightfolding component (LFC) nominally configured to fold light, at leastwhen projected thereon in a direction perpendicular to the firstsurface, at a light folding angle equal to the nominal inclinationangle.

According to some embodiments of the method, the LFC is or includes aprism, one or more mirrors, and/or a diffraction grating.

According to some embodiments of the method, the light folding angle isinsensitive to variations in a pitch of the LFC.

According to some embodiments of the method, the LFC is or includes apentaprism or a like-function prism, or a pair of mirrors set at anangle relative to one another, or a like-function mirror arrangement.

According to some embodiments of the method, the LGA further includes acoupling infrastructure configured to guide the light, folded by LFC,onto or into to the sample, such that light, transmitted thereby intothe sample, nominally normally impinges on the internal facet.

According to some embodiments of the method, the coupling infrastructureincludes a coupling prism (CP). The CP includes an external, flat CPfirst surface, an external, flat CP second surface, nominally inclinedat the nominal angle relative to the CP first surface, and an externalCP third surface, opposite the CP second surface. The CP has a samerefractive index as the first part of the sample or a refractive indexclose to (e.g. to within 0.001%, 0.01%, or even 0.1%, each possibilitycorresponds to separate embodiments) that of the first part of thesample. The CP is disposed such that the CP first surface is parallel tothe first surface of the sample, and is further oriented such that thelight, folded by the LFC, nominally normally impinges on the CP secondsurface.

According to some embodiments of the method, the coupling infrastructurefurther includes a shape-conforming interface. The shape-conforminginterface is disposed between the CP third surface and the sample andhas been made to assume a shape such that the CP first surface isparallel to the first surface of the sample.

According to some embodiments of the method, the shape-conforminginterface has a same refractive index as the first part of the sample ora refractive index close to (e.g. to within 0.001%, 0.01%, or even 0.1%,each possibility corresponds to separate embodiments) that of the firstpart of the sample.

According to some embodiments of the method, the shape-conforminginterface is or includes a liquid and/or a gel.

According to some embodiments of the method, the sample may be a prism,a waveguide, or a beam splitter.

According to some embodiments of the method, the first incident LB andthe second incident LB constitute complementary portions of a singlecollimated light beam or are prepared by blocking off one or more partsof a single collimated light beam.

According to some embodiments of the method, the first incident LB andthe second incident LB are prepared by blocking one or more portions ofa single collimated LB.

According to some embodiments of the method, the single collimated LB ispolychromatic.

According to some embodiments of the method, the single collimated LB isa laser beam.

According to some embodiments of the method, wherein the couplinginfrastructure includes the CP, the method further includes an initialcalibration stage wherein a gold standard sample is utilized tocalibrate orientations of the LFC, the CP, and/or the sample.

According to some embodiments of the method, wherein the couplinginfrastructure includes the CP, the method further includes generatingan additional incident LB, which is directed at the CP first surface andin parallel to the first incident LB. An orientation of the CP is (a)calibrated and/or (b) tested for correct orientation during themeasurement of the first angular deviation, by measuring an additionalangular deviation of an additional returned LB relative to the firstreturned LB. The additional returned LB is obtained by reflection of theadditional incident LB off the first CP surface.

According to some embodiments, the first angular deviation is obtainedfrom measured coordinates of a first spot and a second spot formed bythe first returned LB and the second returned LB, respectively, on aphotosensitive surface of a light sensor.

According to some embodiments of the method, the first angular deviationis measured using an autocollimator.

According to some embodiments of the method, the measured first angulardeviation is equal to Δu/f. Δu is a difference between a coordinate of afirst spot and a corresponding coordinate of a second spot on aphotosensitive surface of the autocollimator. f is a focal length of acollimating lens of the autocollimator. The first spot is formed by thefirst returned LB and the second spot is formed by the second returnedLB.

According to some embodiments of the method, wherein the couplinginfrastructure includes the CP, the actual inclination angle of theinternal facet relative to the first surface is obtained from themeasured first angular deviation, and the values of the actualinclination angle of the CP second surface relative to the CP firstsurface, and the refractive index of the first part of the sample, and,optionally, the actual light folding angle of the LFC.

According to some embodiments of the method, the method further includesmeasuring the actual light folding angle of the LFC.

According to some embodiments of the method, wherein the couplinginfrastructure includes the CP, the method further includes measuringthe actual inclination angle of the CP second surface relative to the CPfirst surface.

According to some embodiments of the method, the nominal inclinationangle is obtuse.

According to some embodiments of the method, the nominal inclinationangle is acute.

According to some embodiments of the method, the nominal inclinationangle is 90° and the sample includes an external third surface, which isflat and parallel to the first surface of the sample. The method furtherincludes, following the measuring of the first angular deviation:

-   -   Flipping the sample, so as to invert the first and third        surfaces.    -   Generating a third incident LB, directed at the third surface        perpendicularly thereto, and a fourth incident LB, parallel to        the third incident LB and directed at the LGA.    -   Obtaining a third returned LB by reflection of the third        incident LB off the second surface.    -   Obtaining a fourth returned LB by redirection by the LGA of the        second incident LB into or onto the sample, reflection thereof        off the internal facet, and inverse redirection by the LGA.    -   Measuring a second angular deviation of the fourth returned LB        relative to the third returned LB.    -   Deducing an actual inclination angle between the first external        surface and the internal facet, based on the measured first        angular deviation and the measured second angular deviation.

According to some embodiments of the method, wherein the couplinginfrastructure includes the CP, the CP further includes a CP fourthsurface opposite and parallel to the CP first surface. The flipping thesample is accompanied by flipping of the CP, such that the CP firstsurface and CP fourth surface are inverted while maintaining a nominalorientation of the CP second surface relative to the sample.

According to some embodiments of the method, an uncertainty in theparallelism of the first surface of the sample and the third surface ofthe sample is smaller, or even significantly smaller (e.g. by an orderof a magnitude or more), than a required measurement precision of theactual inclination angle. According to some embodiments of the method,wherein the coupling infrastructure includes the CP, the actualinclination angle of the internal facet relative to the first surface isobtained from the measured first angular deviation, and the values ofthe actual inclination angle of the CP second surface relative to the CPfirst surface and the refractive index of the first part of the sample.

According to some embodiments of the method, wherein the couplinginfrastructure includes the CP, the actual inclination angle is equalto, or about equal to, 90°+(δ₁−δ₂)/(4n)+Δμ^(m)·(n−1)/n (e.g. the deducedactual inclination angle is between90°+0.95·[(δ₁−δ₂)/(4n)+Δμ^(m)·(n−1)/n)] and90°+1.05·[(δ₁−δ₂)/(4n)+Δμ^(m)·(n−1)/n)], between90°+0.9·[(δ₁−δ₂)/(4n)+Δμ^(m)·(n−1)/n)] and90°+1.1·[(δ₁−δ₂)/(4n)+Δμ^(m)(n−1)/n)], or even between90°+0.8·[(δ₁−δ₂)/(4n)+Δμ^(m)·(n−1)/n)] and90°+1.2·[(δ₁−δ₂)/(4n)+Δμ^(m)(n−1)/n)], each possibility corresponds toseparate embodiments). δ₁ and δ₂ are the measured first angulardeviation and the measured second angular deviation, respectively. n isa refractive index of the first part of the sample. Δμ^(m) is adeviation from 90° in an inclination of the CP second surface relativeto the CP first surface. Advantageously, according to some suchembodiments, knowledge or measurement of the deviation of the actuallight folding angle of the LFC from nominal inclination angle thereof isnot required.

According to some embodiments of the method, the internal facet extendsuntil the first surface of the sample.

According to some embodiments of the method, the sample includes k≥1additional internal facets nominally parallel to the internal facet. Inthe obtaining of the second returned LB, k additional returned LBs areobtained by reflection of k LBs off of each of the k additionalinternals facets, respectively. The k LBs constitute a portion of thesecond incident LB, transmitted into the sample and further transmittedvia the internal facet. In the measuring of the first angular deviation,k additional angular deviations of the k additional returned LBsrelative to the first returned LB are measured. In deducing the actualinclination angle μ′ of the internal facet, (i) k additional actualinclination angles of each of the k additional internal facets areadditionally deduced, and/or (ii) an average actual inclination angleequal to, or about equal to, an average over the actual inclinationangles of internal facet and the k additional internal facets, isdeduced. The average actual inclination angle is indicative of theactual inclination angle μ′ of the internal facet.

According to some embodiments of the method, k≥2. A first of theadditional internal facets is positioned between the internal facet anda second of the additional internal facets. For each m such that2≤m≤k−1, an m-th of the k additional internal facets is positionedbetween an (m−1)-th and an (m+1)-th of the k additional internal facets.According to some such embodiments, each of k+1 spots formed on aphotosensitive surface of a light or image sensor by the second returnedLB and the k additional returned LBs, respectively, may be attributed to(i.e. identified as formed by) the respective returned LB based on thebrightness of the spots. The brightest of the k+1 spots may beattributed to the second returned LB, and for each j, such that 2≤j≤k+1,a j-th brightest spot may be attributed to the returned LB induced byreflection off the (j−1)-th of the k additional internal facets.

According to some embodiments of the method, each of the internal facetand the k additional internal facets is configured to reflect light at arespective spectrum. Each spectrum is distinct from the other spectra,so as to allow distinguishing between each of the second returned LB andthe k additional returned LBs.

According to an aspect of some embodiments, there is provided anoptical-based system for validating an orientation of an internal facetof a sample relative to an external, flat surface of the sample. Thesystem includes:

-   -   A light guiding arrangement (LGA) configured to redirect light,        which is incident on the LGA in a direction perpendicular to an        external and flat first surface of a sample, into or onto the        sample, such that light, transmitted thereby into the sample,        impinges on an internal facet of the sample nominally normally        to the internal facet.    -   An illumination and collection arrangement (ICA) including:        -   A light generation assembly configured to (a) project a            first incident light beam (LB) on the first surface, so as            to generate a first returned LB by reflection off the first            surface, and (b) project a second incident LB on the LGA, in            parallel to the first incident LB, so as generate a second            returned LB, by redirection by the LGA of the second            incident LB into or onto the sample, reflection thereof off            the internal facet, and inverse redirection by the LGA.        -   At least one sensor, configured to measure a first angular            deviation of the second returned LB relative to the first            returned LB, and/or an eyepiece assembly configured to            enable manually measuring the first angular deviation.

The measured first angular deviation is indicative of an actualinclination angle of the internal facet relative to the first surface.

According to some embodiments of the system, the light generationassembly includes a light source and optical equipment.

According to some embodiments of the system, the at least one sensorincludes one or more light sensors and/or one or more image sensors(e.g. one or more cameras).

According to some embodiments of the system, the sample includes a firstpart and a second part, between which the internal facet extends. Thefirst part is positioned between an external second surface of thesample and the internal facet. The LGA is configured to redirect the LGAinto or onto the first part via the second surface.

According to some embodiments of the system, the LGA includes a lightfolding component (LFC) nominally configured to fold light, at leastwhen projected thereon in a direction perpendicular to the firstsurface, at a light folding angle equal to the nominal inclinationangle.

According to some embodiments of the system, the LFC is or includes aprism, one or more mirrors, and/or a diffraction grating.

According to some embodiments of the system, the light folding angle ofthe LFC is insensitive to variations in a pitch of the LFC.

According to some embodiments of the system, the LFC is or includes apentaprism or a like-function prism, or a pair of mirrors set at anangle relative to one another or a like-function mirror arrangement.

According to some embodiments of the system, the LGA further includes acoupling infrastructure configured to guide the light, folded by theLFC, onto or into to the sample, such that light, transmitted therebyinto the sample, nominally normally impinges on the internal facet.

According to some embodiments of the system, the coupling infrastructureincludes a coupling prism (CP), including an external, flat CP firstsurface, an external, flat CP second surface, nominally inclined at thenominal angle relative to the CP first surface, and an external CP thirdsurface (which may be flat or not), opposite the CP second surface. TheCP has a same refractive index as the first part of the sample or arefractive index close to (e.g. to within 0.001%, 0.01%, or even 0.1%,each possibility corresponds to separate embodiments) that of the firstpart of the sample. The CP is disposed such that the CP first surface isparallel to the first surface of the sample, and is further orientedsuch that the light, folded by the LFC, nominally normally impinges onthe CP second surface.

According to some embodiments of the system, the coupling infrastructurefurther includes a shape-conforming interface. The shape-conforminginterface is disposed between the CP third surface and the sample, suchthat the CP first surface is parallel to the first surface of thesample. The shape-conforming interface has a same refractive index asthe first part of the sample or a refractive index close to (e.g. towithin 0.001%, 0.01%, or even 0.1%, each possibility corresponds toseparate embodiments) that of the first part of the sample.

According to some embodiments of the system, the shape-conforminginterface is or includes a liquid and/or a gel.

According to some embodiments of the system, the sample may be a prism,a waveguide, or a beam splitter.

According to some embodiments of the system, wherein the LGA includesthe at least one sensor, the system further includes a computationalmodule configured to compute the actual inclination angle, based atleast on the measured first angular deviation.

According to some embodiments of the system, the computational module isfurther configured to compute an uncertainty in the computed value ofthe actual inclination angle, taking into account at least manufacturingtolerances and imperfections of the LGA and the ICA.

According to some embodiments of the system, including the CP, thesystem further includes orienting infrastructure configured to orientthe sample such that the first incident LB normally impinges on thefirst surface, and/or a folded LB, obtained by folding of the secondincident LB by the LFC, nominally normally impinges on the CP secondsurface.

According to some embodiments of the system, the system further includesan autocollimator. The autocollimator includes the light source, the atleast one sensor, and a collimating lens or collimating lens assembly.

According to some embodiments of the system, the ICA further includes atleast two shutters configured to selectively block each of the incidentLBs, and/or one or more spectral filters configured to at leastfacilitate distinguishing between the returned LBs.

According to some embodiments of the system, wherein the sample includesthe first part and the second part, the nominal inclination angle is 90°and the sample further includes an external, flat third surface, whichis parallel to the first surface.

According to some embodiments of the system, the system is configured tofacilitate flipping the sample.

According to some embodiments of the system, including the at least onesensor and the computational module, the computational module isconfigured to compute the actual inclination angle additionally takinginto account a measured second angular deviation of a fourth returned LBrelative to a third returned LB. With the sample flipped, such that thefirst surface and the third surface are inverted: (a′) The thirdreturned LB is obtained by projecting a third incident light beam on thethird surface of the sample, so as to generate the third returned LB byreflection off the third surface, and (b′) and the fourth returned LB isobtained by projecting a fourth incident LB on the LFC, in parallel tothe third incident LB, so as generate the fourth returned LB, byredirection by the LGA of the fourth incident LB into or onto thesample, reflection thereof off the internal facet, and inverseredirection by the LGA.

According to some embodiments of the system, including the CP, the CPfurther includes an external, flat CP fourth surface, which is parallelto the CP first surface. The CP is mechanically flippable, such that theCP first surface and the CP fourth surface may be inverted, whilemaintaining a nominal orientation of the CP second surface relative tothe sample.

According to some embodiments of the system, the measured second angulardeviation is obtained with the CP flipped, such that the CP firstsurface and the CP fourth surface are inverted and the nominalorientation of the CP second surface relative to the sample ismaintained.

According to some embodiments of the system, wherein the system includesthe orienting infrastructure, the computational module is configured tocompute the uncertainty in the computed value of the actual inclinationangle additionally taking into account manufacturing tolerances andimperfections of the orienting infrastructure.

According to some embodiments of the system, wherein the lightgeneration assembly includes a light source and optical equipment, thelight source is configured to generate a single LB, and the opticalequipment is configured to collimate the single LB.

According to some embodiments of the system, the first incident LB andthe second incident LB are complementary portions of the collimated LB.

According to some embodiments of the system, the light source is apolychromatic light source.

According to some embodiments of the system, the light source isconfigured to generate a laser beam.

Certain embodiments of the present disclosure may include some, all, ornone of the above advantages. One or more other technical advantages maybe readily apparent to those skilled in the art from the figures,descriptions, and claims included herein. Moreover, while specificadvantages have been enumerated above, various embodiments may includeall, some, or none of the enumerated advantages.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure pertains. In case of conflict, thepatent specification, including definitions, governs. As used herein,the indefinite articles “a” and “an” mean “at least one” or “one ormore” unless the context clearly dictates otherwise.

Unless specifically stated otherwise, as apparent from the disclosure,it is appreciated that, according to some embodiments, terms such as“processing”, “computing”, “calculating”, “determining”, “estimating”,“assessing”, “gauging” or the like, may refer to the action and/orprocesses of a computer or computing system, or similar electroniccomputing device, that manipulate and/or transform data, represented asphysical (e.g. electronic) quantities within the computing system'sregisters and/or memories, into other data similarly represented asphysical quantities within the computing system's memories, registers orother such information storage, transmission or display devices.

Embodiments of the present disclosure may include apparatuses forperforming the operations herein. The apparatuses may be speciallyconstructed for the desired purposes or may include a general-purposecomputer(s) selectively activated or reconfigured by a computer programstored in the computer. Such a computer program may be stored in acomputer readable storage medium, such as, but not limited to, any typeof disk including floppy disks, optical disks, CD-ROMs, magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs),electrically programmable read-only memories (EPROMs), electricallyerasable and programmable read only memories (EEPROMs), magnetic oroptical cards, or any other type of media suitable for storingelectronic instructions, and capable of being coupled to a computersystem bus.

The processes and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct a more specializedapparatus to perform the desired method(s). The desired structure(s) fora variety of these systems appear from the description below. Inaddition, embodiments of the present disclosure are not described withreference to any particular programming language. It will be appreciatedthat a variety of programming languages may be used to implement theteachings of the present disclosure as described herein.

Aspects of the disclosure may be described in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by a computer. Generally, program modules include routines,programs, objects, components, data structures, and so forth, whichperform particular tasks or implement particular abstract data types.Disclosed embodiments may also be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotecomputer storage media including memory storage devices.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the disclosure are described herein with referenceto the accompanying figures. The description, together with the figures,makes apparent to a person having ordinary skill in the art how someembodiments may be practiced. The figures are for the purpose ofillustrative description and no attempt is made to show structuraldetails of an embodiment in more detail than is necessary for afundamental understanding of the disclosure. For the sake of clarity,some objects depicted in the figures are not drawn to scale. Moreover,two different objects in the same figure may be drawn to differentscales. In particular, the scale of some objects may be greatlyexaggerated as compared to other objects in the same figure.

In the figures:

FIG. 1A schematically depicts an optical-based system for internal facetmetrology of samples, during inspection of a sample, according to someembodiments;

FIG. 1B schematically depicts trajectories of light beams inside a lightguiding arrangement of the system and the sample, according to someembodiments;

FIG. 1C schematically depicts spots on a photosensitive surface of asensor of the system of FIG. 1A, according to some embodiments;

FIG. 2 schematically depicts an optical-based system for internal facetmetrology of samples, during inspection of a sample, the systemcorresponds to specific embodiments of the system of FIG. 1A;

FIG. 3 schematically depicts an optical-based system for internal facetmetrology of samples, during inspection of a sample, the systemcorresponds to specific embodiments of the system of FIG. 1A;

FIGS. 4A to 4D present non-limiting examples of samples, which may besubjected to internal facet metrology by the system of FIG. 1A,according to some embodiments;

FIGS. 5A and 5B schematically depicts an optical-based system forverifying perpendicularity of an internal facet of a sample with respectto two external, flat surfaces of the sample, which are parallel, duringinspection of the sample, the system corresponds to specific embodimentsof the system of FIG. 1A;

FIGS. 5C and 5D schematically depict spots on a photosensitive surfaceof a sensor of the system of FIGS. 5A and 5B, according to someembodiments;

FIG. 6A schematically depicts inspection of a sample including a pair ofinternal facets, which are nominally parallel, the inspection isperformed utilizing a system corresponding to specific embodiments ofthe system of FIG. 1A;

FIG. 6B schematically depict spots on a photosensitive surface of asensor of the system utilized to inspect the sample of FIG. 6A,according to some embodiments;

FIG. 7 presents a flowchart of an optical-based method for internalfacet metrology of samples, according to some embodiments;

FIGS. 8A and 8B present a flowchart of an optical-based method forvalidating perpendicularity of an internal facet of a sample withrespect to two external, flat surfaces of the sample, which areparallel, according to some embodiments;

FIG. 9 schematically depicts an optical-based system for internal facetmetrology of samples, during inspection of a sample, according to someembodiments; and

FIG. 10 schematically depicts an optical-based system for internal facetmetrology of samples, during inspection of a sample, according to someembodiments.

DETAILED DESCRIPTION

The principles, uses, and implementations of the teachings herein may bebetter understood with reference to the accompanying description andfigures. Upon perusal of the description and figures present herein, oneskilled in the art will be able to implement the teachings hereinwithout undue effort or experimentation. In the figures, same referencenumerals refer to same parts throughout.

In the description and claims of the application, the words “include”and “have”, and forms thereof, are not limited to members in a list withwhich the words may be associated.

As used herein, the term “about” may be used to specify a value of aquantity or parameter (e.g. the length of an element) to within acontinuous range of values in the neighborhood of (and including) agiven (stated) value. According to some embodiments, “about” may specifythe value of a parameter to be between 80% and 120% of the given value.For example, the statement “the length of the element is equal to about1 m” is equivalent to the statement “the length of the element isbetween 0.8 m and 1.2 m”. According to some embodiments, “about” mayspecify the value of a parameter to be between 90% and 110% of the givenvalue. According to some embodiments, “about” may specify the value of aparameter to be between 95% and 105% of the given value.

As used herein, according to some embodiments, the terms “substantially”and “about” may be interchangeable.

For ease of description, in some of the figures a three-dimensionalcartesian coordinate system is introduced. It is noted that theorientation of the coordinate system relative to a depicted object mayvary from one figure to another. Further, the symbol

may be used to represent an axis pointing “out of the page”, while thesymbol {circle around (x)} may be used to represent an axis pointing“into the page”.

In the figures, optional elements and optional stages (in flowcharts)are delineated by a dashed line. Throughout the description, internal,flat surfaces (such as a flat boundary between two parts of athree-dimensional element or an internal flat layer of materialincorporated into a three-dimensional element) of three-dimensionalelements are referred to as “internal facets”.

Systems

According to an aspect of some embodiments, there is provided anoptical-based system for internal facet metrology of samples. FIG. 1Aschematically depicts such a system, an optical-based system 100,according to some embodiments. Optical-based system 100 is configuredfor validating the angle between an internal facet of a sample and anexternal, flat surface of the sample. FIG. 1A presents a cross-sectionalside-view of system 100 and a sample 10, according to some embodiments.(It is to be understood that sample 10 does not constitute a part ofsystem 100.) Sample 10 is shown being inspected by system 100.

Sample 10 includes an external first surface 12 a (i.e. a first externalsurface), an external second surface 12 b (i.e. a second externalsurface), and an internal facet 14. First surface 12 a is flat. Theremaining external surfaces of sample 10 may be of any shape, forexample, curved, so long as their shapes do not preclude positioning andorienting of sample 10, as elaborated on below. As a non-limitingexample, second surface 12 b is depicted as convex, but it is to beunderstood that second surface 12 b may equally be flat, concave, oreven wavy or rough (e.g. unpolished), or include a plurality ofnon-parallel flat surfaces. According to some embodiments, not depictedin FIG. 1A, sample 10 may be shaped as a polyhedron.

Sample 10 is composed at least of a first part 16 a and a second part 16b. According to some embodiments, first part 16 a and second part 16 bshare a common boundary, which is flat, and constituted by internalfacet 14. In such embodiments, first part 16 a and second part 16 b arecharacterized by different refractive indices, respectively (i.e. arefractive index of first part 16 a differs from a refractive index ofsecond part 16 b). As a non-limiting example, according to some suchembodiments, the sample may be an element composed of two glass parts,which are characterized by two different refractive indices,respectively. Alternatively, according to some embodiments, first part16 a and second part 16 b may be separated by a thin and flat layer ofmaterial, or several materials, formed by internal facet 14. The layeris characterized by a different refractive index than at least one offirst part 16 a and second part 16 b (whose refractive indices may ormay not be identical). According to some such embodiments, first part 16a and second part 16 b may be made of the same material, for example, inembodiments wherein sample 10 is a prism or a waveguide and a flat layer(stratum) of material—having a different refractive index than that offirst part 16 a and/or second part 16 b—is incorporated into sample 10between first part 16 a and second part 16 b.

Sample 10 is manufactured to exhibit a (nominal) inclination angle a(indicated in FIG. 1B) between first surface 12 a and internal facet 14.However, due to fabrication imperfections an actual inclination angle α′between first surface 12 a and internal facet 14 will generally differfrom the nominal inclination angle α. A straight (first) dashed line Lis shown in FIG. 1A intersecting internal facet 14 and is inclined atthe nominal inclination angle α relative to first surface 12 a. Thedashed line L indicates the intended inclination of internal facet 14.The nominal inclination angle a may be acute (i.e. α<90°), obtuse (i.e.α>90°), or equal to 90°. A supplementary angle to the actual inclinationangle α′, labelled as β′ (i.e. β′=180°−α′), is indicated in FIG. 1B.

Beyond nominally being inclined at the inclination angle α relative atleast one external, flat surface of sample 10, the orientation ofinternal facet 14 is, in principle not limited. Several differentorientations of internal facets—whose (actual) inclination angles may bemeasured utilizing system 100—within samples sharing the same exteriorgeometry, are described below in the description of FIGS. 4A-4D.

According to some embodiments, first part 16 a may be made of atransparent or semi-transparent material, while second part 16 b may bemade of a transparent material or a semi-transparent material, or evenan opaque material. According to some embodiments, first part 16 a maybe made of glass or crystal (or even transparent or semi-transparentpolymer or metal), while second part 16 b may in principle be made ofany material (including opaque materials). According to someembodiments, wherein first part 16 a and second part 16 b share a commonboundary, first part 16 a and second part 16 b may be glued onto oneanother and/or fused (e.g. laser fused) onto another along the commonboundary thereof.

According to some embodiments, system 100 includes a light guidingarrangement (LGA) 102 and an illumination and collection arrangement (orassembly; ICA) 104. System 100 may further include a controller 108functionally associated with ICA 104 and configured to control operationthereof.

According to some embodiments, and as depicted in FIG. 1A, ICA 104includes a light source 112 (or a plurality of light sources) and asensor 114 (or a plurality of sensors). According to some alternativeembodiments, not depicted in FIG. 1A, ICA 104 includes an eyepieceassembly in place of sensor 114, being thereby configured for visualdetermination (i.e. by eye) of the actual inclination angle.

As described in detail below, ICA 104 is configured to output at leasttwo parallel light beams (LBs) including a first LB 105 a (also referredto as “first incident LB”; indicated in FIG. 1A by a pair of parallellight rays) and a second LB 105 b (also referred to as “second incidentLB”; indicated in FIG. 1A by a pair of parallel light rays).

According to some embodiments, optical equipment 118 may be configuredto collimate light generated by light source 112, and thereby producethe (parallel) incident LBs 105 a and 105 b. According to some suchembodiments, optical equipment 118 may include a collimating lens or acollimating lens assembly (not shown). According to some embodiments,incident LBs 105 a and 105 b may form complementary portions of acollimated light beam (which has been focused by the collimating lens orcollimating lens assembly). Alternatively, according to someembodiments, incident LBs 105 a and 105 b may be spaced apart (andparallel). According to some such embodiments, optical equipment 118,may further include one or more optical filters (e.g. a light absorbingfilter or an opaque plate), and/or one or more beam splitters, and,optionally, one or more mirrors (not shown), configured to prepare fromthe collimated light beam a pair of spaced apart and parallel lightbeams.

According to some embodiments, optical equipment 118 may further includea plurality of blocking elements (such as the blocking elements depictedin FIG. 2 ) configured to allow selectively blocking each of incidentLBs 105 or at least facilitate distinguishing between a first returnedLB 133 a, induced by first incident LB 105, and a second returned LB 133b, induced by second incident LB 105 b. As used herein, the term“blocking element”, with reference to an optical element, is beconstrued broadly as encompassing both controllably openable andclosable opaque elements (such as shutters) configured to (when closed)block light beams incident thereon, and filtering elements (such asspectral filters) configured to block, whether fully or partially, oneor more parts of an optical spectrum (e.g. the visible spectrum).

According to some embodiments, light source 112 may be configured toproduce or allow producing polychromatic light. According to some suchembodiments, the spectrum of the light may be controllable. According tosome embodiments, light source 112 may be configured to produce or allowproducing monochromatic light.

According to some embodiments, ICA 104 is or includes an autocollimator(i.e. light source 112, sensor 114, and some or all of optical equipment118 constitute components of the autocollimator). According to someembodiments, incident LBs 105 constitute adjacent sub-beams of a single,broad, and collimated LB generated by the autocollimator. According tosuch embodiments, optical equipment 118 may include an optical filterconfigured to transmit two sub-beams (such as incident LBs 105) of thecollimated LB, prepared by the autocollimator and incident on theoptical filter (with the parallelism of the two sub-beams beingmaintained on emergence from the optical filter).

According to some embodiments, and as depicted in FIG. 1A, LGA 102includes a light folding component 122 (LFC) and a couplinginfrastructure 124, which may be disposed between LFC 122 and sample 10.LFC 122 is nominally configured to fold light, projected thereon in adirection perpendicular to first surface 12 a, at a light folding angleα″, which is equal to the nominal inclination angle α. (That is,ideally, the light folding angle α″ will be equal to the nominalinclination angle.)

According to some embodiments, LFC 122 may be or include a prism, one ormore mirrors, or a diffraction grating. According to some embodiments,LFC 122 may be a pentaprism (as depicted in FIG. 3 ) or a like-functionprism that is insensitive to variations in pitch (in the sense that thelight folding angle thereof remains unchanged when the pitch of LFC 122is slightly changed, i.e. when LFC 122 is slightly rotated about they-axis). According to some embodiments, LFC 122 may be a pair of mirrorsset at an angle with respect to one another, or a like-functionarrangement of mirrors (i.e. insensitive to variations in pitch).

In embodiments wherein internal facet 14 is (by design) not parallel tosecond surface 12 b, additional infrastructure may be required to causelight—projected (outside of sample 10) on second surface 12 b in adirection perpendicular to internal facet 14—to maintain the propagationdirection thereof after entering into sample 10. The same may apply alsowhen internal facet 14 and second surface 12 b are nominally parallel,since—even if second surface 12 b is sufficiently smooth—due tomanufacturing tolerances, second surface 12 b actual inclination willgenerally slightly differ from the nominal inclination. Couplinginfrastructure 124 is configured to this end, as described below.

According to some embodiments, and as depicted in FIG. 1A, couplinginfrastructure 124 may include a coupling prism (CP) 132 and ashape-conforming interface 134. CP 132 includes an external and flat(CP) first surface 138 a, an external and flat (CP) second surface 138b, and an external (CP) third surface 138 c (which may or may not beflat). CP second surface 138 b is nominally inclined at the nominalinclination angle a relative to CP first surface 138 a, as indicated bya second dashed line L′, which is parallel to the first dashed line L.CP third surface 138 c may be positioned opposite to CP first surface138 a.

According to some embodiments, shape-conforming interface 134 may beconfined between second surface 12 b (of sample 10) and CP third surface138 c, adjacently to each. Shape-conforming interface 134 may be aliquid, gel, or paste characterized by a surface tension and/or adhesiveproperties, such as to maintain integrity and disposition thereof whenconfined in a narrow space. According to some embodiments,shape-conforming interface 134 may be a malleable material. According tosome embodiments, and as depicted in FIG. 1B, the refractive indices ofCP 132 and shape-conforming interface 134 are each equal to, or close to(e.g. to within 0.001%, 0.01%, or even 0.1%, each possibilitycorresponds to separate embodiments), the refractive index of sample 10.According to some embodiments, the values of the refractive indices ofCP 132 and shape-conforming interface 134 are sufficiently small suchthat the overall uncertainty in the measured value of the actualinclination angle α′ does not exceed the required measurement precision.Thus, a light beam propagating through CP 132, shape-conforminginterface 134, and sample 10, will maintain the propagation directionthereof on transitioning from CP 132 to shape-conforming interface 134and on transitioning from shape-conforming interface 134 to sample 10.

According to some embodiments, system 100 may further include orientinginfrastructure 140 for orientating sample 10 relative to ICA 104. As anon-limiting example, orienting infrastructure 140 may include anorientable (first) stage 142 (i.e. a first stage, which may beoriented), which is configured for motion in six degrees of freedom.Stage 142 is configured for mounting thereon a sample, such as sample10. In particular, orienting infrastructure 140 may be configured toorient sample 10, such that first incident LB 105 a will perpendicularlyimpinge on first surface 12 a. According to some embodiments, orientinginfrastructure 140 may be functionally associated with controller 108and is configured to be controlled thereby.

According to some embodiments, orienting infrastructure 140 may befurther configured to orient CP 132 relative to LGA 102, ICA 104, andsample 10. According to some such embodiments, orienting infrastructure140 may include an orientable second stage 144, which is configured tohave placed thereon CP 132 and to rotate CP 132 along each of threenon-parallel axes, and, optionally, translate CP 132.

As used herein, according to some embodiments, the terms “nominally” and“ideally” may be interchangeable. An object may be said to “nominally”exhibit (i.e. be characterized by) an intrinsic property, such as aninclination angle between flat surfaces of the sample, when the objectis intended by design and fabrication to exhibit the property but, inpractice, due to manufacturing tolerances, the object may actually onlyimperfectly exhibit the property. The same applies to an extrinsicproperty of an object, such as the light propagation direction of alight beam. In this case, it is to be understood that the object hasintentionally been prepared, or otherwise manipulated, to ideallyexhibit the property but, in practice, due to inherent imperfections,e.g. in a setup used for the preparation, the object may actually onlyimperfectly exhibit the property.

In operation, first incident LB 105 a is projected on sample 10,normally to first surface 12 a, and second incident LB 105 b isprojected on LFC 122. First incident LB 105 a (or at least a portionthereof) is reflected off first surface 12 a—as indicated by firstreturned LB 133 a—and is sensed by sensor 114.

Second incident LB 105 b is folded by LFC 122 at the light folding angleα″, as indicated by a folded LB 113 b. The light folding angle α′ isnominally equal to the nominal inclination angle α. However, inpractice, due to manufacturing imperfections, the light folding angle α″of LFC 122 may slightly deviate from the nominal inclination angle α.When the uncertainty in the light folding angle (due to themanufacturing tolerance) of LFC 122 is lower, or significantly lower,than the accuracy to which the actual inclination angle of internalfacet 14 is to be determined, the uncertainty in the light folding anglemay be neglected (i.e. LFC 122 may be assumed to fold second incident LB105 b at precisely the nominal inclination angle α). Otherwise, theuncertainty in the light folding angle may contribute (non-negligibly)to the overall uncertainty in the measured value of the actualinclination angle.

In order to keep the figures uncumbersome, only two light rays of eachlight beam are typically indicated. Further, the depiction of the lightbeams is schematic, and it is to be understood that depicted light beamsmay be wider or narrower than drawn. Thus, for example, according tosome embodiments, first incident LB 105 a may impinge over all of firstsurface 12 a, and/or second incident LB 105 b may impinge over all of alight receiving surface of LFC 122.

Referring also to FIG. 1B, folded LB 113 b travels onto CP 132. Atransmitted LB 117 b indicates a portion of folded LB 113 b, which istransmitted into CP 132 via CP second surface 138 b (a portion of foldedLB 113 b, reflected off CP second surface 138 b, and which may benegligible, is not shown). Transmitted LB 117 b propagates across CP 132from CP second surface 138 b to CP third surface 138 c, next acrossshape-conforming interface 134 from CP third surface 138 c to secondsurface 12 b of sample 10, and, finally, across first part 16 a towardsinternal facet 14.

A reflected LB 121 b indicates a portion of transmitted LB 117 breflected by internal facet 14 back towards shape-conforming interface134 (a portion of transmitted LB 117 b, transmitted from first part 16 ainto second part 16 b, if present, is not shown). Reflected LB 121 bpropagates across first part 16 a towards second surface 12 b, nextacross shape-conforming interface 134 from second surface 12 b to CPthird surface 138 c, and, finally, across CP 132 from CP third surface138 c to CP second surface 138 b. An emerged LB 125 b indicates aportion of reflected LB 121 b, which exits CP 132 via CP second surface138 b (a portion of reflected LB 121 b, internally reflected by CPsecond surface 138 b, is not shown). Emerged LB 125 b travels towardsLFC 122 and is folded thereby at the light folding angle α″, asindicated by second returned LB 133 b. More precisely, emerged LB 125 bis redirected by LFC 122 towards ICA 104 (as indicated by secondreturned LB 133 b). Second returned LB 133 b is sensed by sensor 114.

Transmitted LB 117 b impinges on internal facet 14 at an incidence angleθ. Angles are measured clockwise relative to the point-of-view of areader perusing the figures. Values of angles greater than 180° are setto negative by subtracting 360°. Thus, as a non-limiting exampleintended to facilitate the description by making it more concrete, inFIG. 1B, the incidence angle θ is negative and a return angle θ_(R)(i.e. the reflection angle) is positive. More precisely, the incidenceangle θ is shown spanned counter-clockwise from a dotted line B—whichindicates a normal to second surface 12 b—to a light ray 117 b 1 (one ofthe two light rays indicating transmitted LB 117 b). The inclinationangles α and α′ are measured clockwise from first surface 12 a (as anon-limiting example, intended to facilitate the description, in FIG. 1Aα′ is shown as being greater than α).The nominal inclination angle α isspanned clockwise from first surface 12 a to the dashed line L. Theactual inclination angle α′ is spanned clockwise from first surface 12 ato internal facet 14.

The incidence angle θ depends on each of the deviations Δα′=α−α′ (i.e.the deviation in the inclination of internal facet 14 from the nominalinclination), Δα″=α−α″ (i.e. the deviation of the (actual) light foldingangle of LFC 122 from α), and Δα′″=α−α′″ (i.e. the deviation in theinclination of CP second surface 138 b from the nominal inclination).Absent any imperfections in system 100 (i.e. α′″=α″=α), and with CPfirst surface 138 a being oriented in parallel to first surface 12 a,the incidence angle θ would equal Δα′. Put differently, the incidenceangle θ equals Δα′ to a precision dependent on the uncertainties in thelight folding angle α″ and actual inclination angle α″' and any otherrelevant uncertainties in parameters of LGA 102, ICA 104, and orientinginfrastructure 140 (i.e. the orientation precision thereof). Inparticular, system 100 is nominally configured to have transmitted LB117 b normally (i.e. perpendicularly) impinge on internal facet 14 whenΔα′=0. A normal to internal facet 14 is indicated in FIG. 1B by a(straight) dotted line B.

Typically, due to the manufacturing imperfections of both sample 10 andLGA 102, second returned LB 133 b will not be parallel to first returnedLB 133 a. An angle δ—also referred to as “the angular deviation”—betweenfirst returned LB 133 a and second returned LB 133 b depends on thedeviations Δα′, Δα″, and Δα′″, and a refractive index n of the firstpart 16 a (which is equal to the refractive indices of CP 132 andshape-conforming interface 134 or close to the refractive indicesthereof). The angle δ is shown spanned clockwise from a light ray 105 b1 (one of the two light rays indicating second incident LB 105 b) to alight ray 133 b 1 (one of the two light rays indicating second returnedLB 133 b) and is therefore positive in FIG. 1A.

The angle δ may be related to Δα′ using the laws of geometrical opticsand, in particular, Snell's law (and taking into account the actuallight folding angle of LFC 122, the actual inclination angle of CPsecond surface 138 b relative to CP first surface 138 a, and therefractive index n). Put differently, Δα′ depends on Δα″, Δα′″, themeasured value of the angle δ, and the refractive index n.

Referring also to FIG. 1C, FIG. 1C schematically depicts a first spot147 a and a second spot 147 b formed by first returned LB 133 a andsecond returned LB 133 b, respectively, on a photosensitive surface 148of sensor 114, according to some embodiments. u₁ and u₂ are thehorizontal coordinates (i.e. as measured along the x-axis) of first spot147 a and second spot 147 b, respectively. (The coordinate systemdepicted in FIG. 1C is assumed to coincide with the coordinate systemdepicted in FIG. 1A up to a possible translation of the origin. Thex-axis in FIG. 1C thus extends from second incident LB 105 b to firstincident LB 105 a in parallel to first surface 12 a.) The angle δ may bedirectly inferred from the difference Δu=u₂−u₁. As a non-limitingexample, when the measurement is autocollimator-based (i.e. inembodiments wherein ICA 104 is or includes an autocollimator), δ=Δu/f.

According to some embodiments, controller 108 may be communicativelyassociated with a computational module 130. Computational module 130 mayinclude a processor(s) and volatile and/or non-volatile memorycomponents. The processor may be configured to receive from controller108 sensor 114 data (i.e. the values of u₁ and u₂), and, based thereon,compute Δα′. Optionally, according to some embodiments, the processormay further be configured to compute an uncertainty in the (computedvalue of) Δα′ taking into account manufacturing tolerances andcalibration limitations of LGA 102 (including the uncertainty in theactual light folding angle), ICA 104, and orienting infrastructure 140.According to some embodiments, computational module 130 may be includedin system 100.

According to some embodiments, light source 112 may be configured toproduce a collimated (first) laser beam. According to some suchembodiments, optical equipment 118 may include a beam expander (notshown) configured increase the diameter of the laser beam, such that theexpanded laser beam may simultaneously impinge on both sample 10 and LFC122. In such embodiments, first incident LB 105 a and second incident LB105 b may constitute complementary portions of the laser beam.Alternatively, optical equipment 118 may include a beam splitter andoptics configured to divide the laser beam into a pair of parallel(spaced apart) sub-beams: a first sub-beam and a second sub-beam, whichconstitute first incident LB 105 a and second incident LB 105 b,respectively.

According to some such embodiments, optical equipment 118 may beconfigured to recombine the returned sub-beams (i.e. first returned LB133 a and second returned LB 133 b), such that the sub-beams areredirected onto a single light sensor (i.e. sensor 114 according to someembodiments thereof). Ideally, if the second sub-beam (after redirectionby LFC 122 and transmission into sample 10) perpendicularly impinges oninternal facet 14, then the recombined sub-beams will form a collimated(second) laser beam, and the two spots, formed by the recombinedsub-beams on the light sensor, will overlap. According to some otherembodiments, two light sensors—such that the distance and the relativeorientation therebetween, is known—may be employed. In such embodiments,each of the returned sub-beams may be directed to a different lightsensor from the two light sensors.

According to some alternative embodiments, ICA 104 may be configured forinterferometry. That is, light source 112, some or all of opticalequipment 118, and sensor 114 may constitute components of aninterferometric setup, as described below. In such embodiments, lightsource 112 may be configured to generate a coherent, planar wavefront.Optical equipment 118 may be configured to split the generated wavefrontinto two wavefronts: a first (coherent, planar) incident wavefront and asecond (coherent, planar) incident wavefront, which constitute firstincident LB 105 a and second incident LB 105 b, respectively. In suchembodiments, the angle δ may be deduced from an interference patternformed by first returned LB 133 a and second returned LB 133 b. Morespecifically, in such embodiments, first returned LB 133 a constitutes afirst returned wavefront, obtained from reflection of the first incidentwavefront off first surface 12 a, and second returned LB 133 bconstitutes a second returned wavefront, obtained by folding of thesecond incident wavefront by LFC 122, reflection off internal facet 14,and folding again by LFC 122. The returned wavefronts are recombined andan interference pattern thereof is measured by sensor 114. If the firstwavefront and the second wavefront impinge normally on the respectivesurface (i.e. first surface 12 a or internal facet 14, respectively),the recombined wavefront will form a uniform pattern on sensor 114. Ifsecond surface 12 b deviates from the nominal inclination, then therecombined wavefront will form a periodic pattern on sensor 114. Thedeviation Δα′ may be deduced from the periodicity of the pattern.

According to some embodiments, system 100 may further include twoshutters configured to allow selectively blocking each of first returnedLB 133 a and second returned LB 133 b, so that each of returned LBs 133may be separately sensed (thereby facilitating attributing each of spots147 to the returned LB that induced the spot).

According to some embodiments, first surface 12 a may be coated, ortemporarily coated, by a reflective coating, so that light incidentthereon is maximally reflected or reflection therefrom is at leastincreased. According to some embodiments, CP second surface 138 b may becoated by an anti-reflective coating, so that external light incidentthereon is maximally transmitted into CP 132 and internal light incidentthereon is maximally transmitted out of CP 132. According to someembodiments, wherein light source 112 is configured to generatepolychromatic light, first surface 12 a may be coated by a first coatingconfigured to reflect light in a first spectrum, and CP second surface138 b (or LFC 122 or internal facet 14) may be coated by a secondcoating configured to reflect light in a second spectrum, which doesnot, or substantially does not, overlap with the first spectrum. In suchembodiments, selective blocking of first returned LB 133 a and secondreturned LB 133 b may be implemented using a spectral filter or aspectral filter arrangement (optionally, instead of shutters),positioned such that each of returned LBs 133 is incident thereon andconfigured to allow selectively blocking or at least partially blockinglight in the second spectrum and first spectrum, respectively.

According to some alternative embodiments, a first (passive) spectralfilter may be employed to filter first incident LB 105 a into the firstspectrum, and a second (passive) spectral filter may be employed tofilter second incident LB 105 b into the second spectrum. In suchembodiments, in order to allow separately sensing each of returned LBs133, an additional spectral filter, positioned between the spectralfilters and sensor 114, and configured to allow selectively filteringtherethrough light either in the first spectrum or the second spectrum,may be employed.

It is noted that the spectral filter or the spectral filter arrangementmay be used to decrease the signal associated with stray light,associated with any one of incident LBs 105, arriving at sensor 114.

While in FIG. 1A, internal facet 14 is shown as sectioning (i.e.dividing in two) sample 10, and, in particular, extending until firstsurface 12 a, it is to be understood that scope of the disclosure is notlimited to metrology of so shaped samples: Any sample including anexternal, flat surface and an internal facet, which is inclined withrespect to the external, flat surface, but which does not extend untilthe external, flat surface, may also undergo internal facet metrologyutilizing system 100, as described above.

FIG. 2 schematically depicts an optical-based system 200 for validatingan angle between an internal facet of a sample and an external, flatsurface of the sample, according to some embodiments. System 200corresponds to specific embodiments of system 100. More specifically,FIG. 2 provides a side-view of system 200 and sample 10 being inspectedby system 200, according to some embodiments. System 200 includes a LGA202, and an ICA 204, which correspond to specific embodiments of LGA 102and ICA 104. According to some embodiments, and as depicted in FIG. 2 ,system 200 may further include an orienting infrastructure 240, acontroller 208, and, optionally, a computational module 230. Orientinginfrastructure 240, controller 208, and computational module 230correspond to specific embodiments of orienting infrastructure 140,controller 108, and computational module 130, respectively. Orientinginfrastructure 240 may include a first stage 242 and a second stage 244,which correspond to specific embodiments of first stage 142 and secondstage 144, respectively.

According to some embodiments, ICA 204 includes an autocollimator 250.Autocollimator 250 may be configured to generate a collimated, broad LB201 in a direction perpendicular to first surface 12 a of sample 10. Afirst incident LB 205 a and a second incident LB 205 b constitute afirst sub-beam and a second sub-beam, respectively, of LB 201. Firstincident LB 205 a and second incident LB 205 b correspond to specificembodiments of first incident LB 105 a and second incident LB 105 b,respectively. Also indicated are a folded LB 213 b and an emerged LB 225b, which correspond to specific embodiments of folded LB 113 b andemerged LB 125 b, respectively.

LGA 202 includes a LFC 222 and a coupling infrastructure 224, whichcorrespond to specific embodiments of LFC 122 and couplinginfrastructure 124, respectively. According to some embodiments, and asdepicted in FIG. 2 , coupling infrastructure 224 includes a CP 232 and ashape-conforming interface 234, which correspond to specific embodimentsof CP 132 and shape-conforming interface 134, respectively. CP 232includes a CP first surface 238 a, a CP second surface 238 b, and a CPthird surface 238 c, which correspond to specific embodiments of CPfirst surface 138 a, CP second surface 138 b, and CP third surface 138c, respectively, of CP 132.

Additional incident LB 205 s may be used to (nominally) orient CP secondsurface 238 b in parallel to internal facet 14. More specifically,additional incident LB 205 s may be used to ensure parallelism of a CPfirst surface 238 a of CP 232 and first surface 12 a (on which firstincident LB 205 a normally impinges) of sample 10, since when CP firstsurface 238 a is oriented in parallel to first surface 12 a, additionalincident LB 205 s will normally impinge on CP first surface 238 a. Thus,by measuring an angular deviation of an additional returned LB 233s—obtained by the reflection of additional incident LB 205 s off CPfirst surface 238 a—relative to first returned LB 233 a, the orientationof CP first surface 238 a may be adjusted (by rotating second stage 244and/or first stage 242) until parallelism thereof relative to firstsurface 12 a is attained. With CP first surface 238 a being disposed inparallel to first surface 12 a, (nominal) parallelism of CP secondsurface 238 b and internal facet 14 may be achieved by rotating CP 232about an axis parallel to the z-axis.

According to some embodiments, and as depicted in FIG. 2 , opticalequipment of ICA 204 may include a pair of blocking elements 256 a and256 b, allowing to selectively block each of first incident LB 205 a andsecond incident LB 205 b or at least facilitate distinguishing betweenfirst returned LB 233 a and second returned LB 233 b. According to somesuch embodiments, and wherein ICA 204 is further configured to generateadditional incident LB 205 s, the optical equipment may further includea third blocking element 256 s configured to allow selectively blockingadditional incident LB 205 s or at least facilitate distinguishingadditional returned LB 233 s from first returned LB 233 a and secondreturned LB 233 b.

According to some embodiments, each of blocking elements 256 a and 256b, and blocking element 256 s (when included) may be a shutter.

According to some embodiments, first surface 12 a may be coated, ortemporarily coated, by a reflective coating, so that light incidentthereon is maximally reflected or reflection therefrom is at leastincreased. According to some embodiments, CP second surface 238 b may becoated by an anti-reflective coating, so that light incident thereon ismaximally transmitted into CP 232 or transmission thereto is at leastincreased. According to some embodiments, CP first surface 238 a may becoated by a reflective coating, so that light incident thereon ismaximally reflected or reflection therefrom is at least increased.

According to some embodiments (wherein autocollimator 250 is configuredto produce polychromatic light), first surface 12 a may be coated by afirst coating configured to reflect light in a first spectrum, and CPsecond surface 238 b may be coated by a coating configured to transmitinto CP 232 light in a second spectrum, which differs from the firstspectrum, so as to facilitate distinguishing between first returned LB233 a and second returned LB 233 b, and/or internal facet 14 may beconfigured to reflect light at the second spectrum (and at leastpartially transmit light in the first spectrum). According to some suchembodiments, a spectral filter or spectral filter arrangement (e.g.included in autocollimator 250), configured to allow controllablyfiltering therethrough light in the first spectrum or the secondspectrum, may be employed to facilitate separately sensing each ofreturned LBs 233.

According to some embodiments, wherein ICA 204 is further configured togenerate additional incident LB 205 s, CP first surface 238 a may becoated by a third coating configured to reflect light in a thirdspectrum differing from each of the first spectrum and second spectrum,so as to facilitate distinguishing additional returned LB 233 s fromeach of first returned LB 233 a and second returned LB 233 b. In suchembodiments, the spectral filter or spectral filter arrangement (e.g.included in autocollimator 250) may be further configured to allowcontrollably filtering therethrough light in the third spectrum.

According to some embodiments, blocking elements 256 a and 256 b may be(passive) spectral filters (a specific example being dichroic filter)configured to filter therethrough light in the first spectrum and thesecond spectrum, respectively. In such embodiments, in order to allowseparately sensing each of returned LBs 233, an additional spectralfilter, positioned between blocking elements 256 and autocollimator 250or included in autocollimator 250, and configured to allow selectivelyfiltering therethrough either light in the first spectrum or the secondspectrum, may be employed.

FIG. 3 schematically depicts an optical-based system 300 for validatingthe angle between an internal facet of a sample and an external, flatsurface of the sample, according to some embodiments. System 300corresponds to specific embodiments of system 100, wherein the LFC is orincludes a prism. More specifically, FIG. 3 provides a side-view ofsystem 300 and sample 10 being inspected by system 300. System 300includes a LGA 302 and an ICA 304 (components thereof are not shown),which correspond to specific embodiments of LGA 102 and ICA 104.According to some embodiments, and as depicted in FIG. 3 , system 300may further include a controller 308, an orienting infrastructure 340,and, optionally, a computational module 330. Orienting infrastructure340, controller 308, and computational module 330 correspond to specificembodiments of orienting infrastructure 140, controller 108, andcomputational module 130, respectively.

LGA 302 includes a prism 322 and a coupling infrastructure 324 includinga CP 332 and a shape-conforming interface 334. Prism 322 corresponds tospecific embodiments of LFC 122. CP 332 and shape-conforming interface334 correspond to specific embodiments of CP 132 and shape-conforminginterface 134. CP 332 includes a CP first surface 338 a, a CP secondsurface 338 b, and a CP third surface 338 c.

According to some embodiments, prism 322 may be insensitive tovariations in pitch—i.e. rotations about the y-axis—at least across acontinuous range of pitch angles. According to some such embodiments,and as depicted in FIG. 3 , prism 322 may be a pentaprism, or alike-function prism—e.g. a prism including an even number of internallyreflecting surfaces. According to some alternative embodiments, notdepicted in FIG. 3 , instead of prism 322, LGA 302 may include twomirrors, nominally set with respect to one another at the same angle atwhich the two surfaces of prism 322 (a pentaprism first surface 328 aand a pentaprism second surface 328 b), which internally reflect atransmitted portion of second incident LB 305 b, are set.

Shown in FIG. 3 are a first incident LB 305 a, a first returned LB 333a, a second incident LB 305 b, a folded LB 313 b, a transmitted LB 317b, a reflected LB 321 b, an emerged LB 325 b, and a second returned LB333 b, which correspond to specific embodiments of first incident LB 105a, first returned LB 133 a, second incident LB 105 b, folded LB 113 b,transmitted LB 117 b, reflected LB 121 b, emerged LB 125 b, and secondreturned LB 133 b, respectively. Also shown in FIG. 3 are thetrajectories of second incident LB 305 b and emerged LB 325 b insideprism 322 after entry thereof thereinto. Penetrating portions of secondincident LB 305 b after transmission into prism 322, after reflectiontherein, and after two reflections therein, are numbered 309 b 1, 309 b2, and 309 b 3, respectively. Penetrating portions of emerged LB 325 bafter refraction into prism 322, after reflection therein, and after tworeflections therein, are numbered 329 b 1, 329 b 2, and 329 b 3,respectively.

FIGS. 4A-4D present examples of internal facet orientation withinsamples, according to some embodiments. The depicted samples arenon-limiting and are intended to illustrate by way of specific examplesthat system 100 capacity is, in principle, not limited so long as thesample includes: (i) an external (first) surface, which is flat; (ii) aninternal facet set at angle relative to the first surface; and (iii) afirst part, which is positioned between an external second surface ofthe sample and the internal facet, which is characterized by a uniformrefractive index, and which affords a continuous, straight path for alight beam, transmitted into the sample via the second surface, tonormally impinge on the internal facet.

Referring to FIG. 4A, a sample 40 is depicted, according to someembodiments. Sample 40 includes an external, flat first surface 42 a, anexternal second surface 42 b, and an internal facet 44. Second surface42 b is positioned opposite to internal facet 44. A first part 46 a ofsample 40, characterized by a uniform refractive index, is partiallybounded by second surface 42 b and internal facet 44. Internal facet 44is nominally inclined at 90° relative to first surface 42 a. Accordingto some embodiments, and as depicted in FIG. 4A, second surface 42 b maybe flat and nominally oriented in parallel to internal facet 44. Sample40 further includes an external third surface 42 c positioned oppositeto first surface 42 a, and an external fourth surface 42 d positionedbetween first surface 42 a and third surface 42 c and sharing a commonedge with second surface 42 b.

Also shown is a CP 432 of a system (of which only CP 432 is shown) forinternal facet metrology of samples, which corresponds to specificembodiments of system 100. In particular, CP 432 corresponds to specificembodiments of CP 132. CP 432 includes an external and flat CP firstsurface 438 a, an external and flat CP second surface 438 b, and anexternal CP third surface (not numbered). CP second surface 438 b isnominally inclined at the nominal inclination angle relative to CP firstsurface 438 a. CP 432 is oriented such that CP first surface 438 a isparallel to first surface 42 a and CP second surface 438 b is nominallyparallel to internal facet 44. A shape-conforming interface (not shown)may be disposed between the CP third surface and second surface 42 b.

When sample 40 undergoes inspection, according to the teachingsdisclosed herein, an incident LB is folded by a LFC such as to nominallynormally impinge on CP second surface 438 b, as described in thedescription of system 100.

According to some embodiments, wherein, as depicted in FIG. 4A, thirdsurface 42 c is flat and parallel to first surface 42 a with anuncertainty in the parallelism of third surface 42 c and first surface42 a being smaller than a required measurement accuracy of theinclination angle, the system depicted in FIGS. 5A and 5B may beutilized to measure the (actual) inclination angle.

Referring to FIG. 4B, a sample 40′ is depicted, according to someembodiments. Sample 40′ includes an external, flat first surface 42 a′,an external second surface 42 b′, and an internal facet 44′. A firstpart 46 a′ of sample 40′, characterized by a uniform refractive index,is partially bounded by second surface 42 b′ and internal facet 44′.Sample 40′ has the same exterior geometry as sample 40 but differstherefrom in an inclination angle (relative to first surface 42 a′) ofinternal facet 44′, which is obtuse. More specifically, the inclinationof internal facet 44′ differs from that of internal facet 44 by rotationabout an axis parallel to the y-axis.

Also shown is a CP 432′ of a system (of which only CP 432′ is shown’)for internal facet metrology of samples, which corresponds to specificembodiments of system 100. In particular, CP 432′ corresponds tospecific embodiments of CP 132. CP 432′ includes an external and flat CPfirst surface 438 a′, an external and flat CP second surface 438 b′, andan external CP third surface (not numbered). CP second surface 438 b′ isnominally inclined at the nominal inclination angle relative to CP firstsurface 438 a′. CP 432′ is oriented such that CP first surface 438 a′ isparallel to first surface 42 a′ and CP second surface 438 b′ isnominally parallel to internal facet 44′. A shape-conforming interface(not shown) may be disposed between the CP third surface and secondsurface 42 b′.

When sample 40′ undergoes inspection, according to the teachingsdisclosed herein, an incident LB is folded by a LFC such as to nominallynormally impinge on CP second surface 438 b′, as described in thedescription of system 100.

Referring to FIG. 4C, a sample 40″ is depicted, according to someembodiments. Sample 40″ includes an external, flat first surface 42 a″,an external second surface 42 b″, an external third surface 42 c″, anexternal fourth surface 42 d″, and an internal facet 44″ nominallyinclined at 90° relative to first surface 42 a. A first part 46 a″ ofsample 40″, characterized by a uniform refractive index, is partiallybounded by second surface 42 b″ and internal facet 44″. Third surface 42c″ is positioned opposite to first surface 42 a″. Fourth surface 42 d″extends between first surface 42 a and second surface 42 b and shares acommon edge with second surface 42 b″. According to some embodiments,and as depicted in FIG. 4C, fourth surface 42 d″ is flat. Sample 40″ hasthe same exterior geometry as sample 40 but differs therefrom in theorientation of internal facet 44″. More specifically, the orientation ofinternal facet 44″ differs from that of internal facet 44 by rotationabout an axis parallel to the z-axis.

Also shown is a CP 432″ of a system (of which only CP 432″ is shown) forinternal facet metrology of samples, which corresponds to specificembodiments of system 100. In particular, CP 432″ corresponds tospecific embodiments of CP 132. CP 432″ includes an external and flat CPfirst surface 438 a″, an external and flat CP second surface 438 b″, andan external CP third surface (not numbered). CP second surface 438 b″ isnominally inclined at the nominal inclination angle relative to CP firstsurface 438 a″. CP 432″ is oriented such that CP first surface 438 a″ isparallel to first surface 42 a″ and CP second surface 438 b″ isnominally parallel to internal facet 44″. A shape-conforming interface(not shown) may be disposed between the CP third surface and secondsurface 42 b″.

When sample 40″ undergoes inspection, according to the teachingsdisclosed herein, an incident LB is folded by a LFC such as to nominallynormally impinge on CP second surface 438 b″, as described in thedescription of system 100.

According to some embodiments, wherein, as depicted in FIG. 4C, thirdsurface 42 c″ is flat and parallel to first surface 42 a with anuncertainty in the parallelism of third surface 42 c″ and first surface42 a″ being smaller than a required measurement accuracy of theinclination angle, the system depicted in FIGS. 5A and 5B may beutilized to measure the (actual) inclination angle.

Referring to FIG. 4D, a sample 40′″ is depicted, according to someembodiments. Sample 40′″ includes an external, flat first surface 42a′″, an external second surface 42 b′″, and an internal facet 44′. Afirst part 46 a′″ of sample 40′″, characterized by a uniform refractiveindex, is partially bounded by second surface 42 b′″ and internal facet44′. Sample 40′″ has the same exterior geometry as sample 40 but differstherefrom in an inclination angle γ (relative to first surface 42 a′″)of internal facet 44′″, which is obtuse, as well as in an orientationrelative to second surface 42 b″. More specifically, the inclination ofinternal facet 44′″ differs from that of internal facet 44 by rotationabout a first axis parallel to an axis s (indicated in FIG. 4C), whichis positioned on the yz-plane about midway between positive y-axis andthe positive z-axis.

A top edge 48 a′″ of internal facet 44′″ extends along first surface 42a′″. Also indicated are: (i) a straight, dashed first line T₁, whichextends along internal facet 44′″ and is perpendicular to top edge 48a′″, (ii) a second straight, dashed second line T₂, which isperpendicular to first surface 42 a′″ and intersects first line T₁ attop edge 48 a′″, and (iii) a straight, dashed third line T₃, whichextends from first line T₁ to second line T₂ in parallel to firstsurface 42 a′″ (and is therefore perpendicular to second line T₂).Finally, the inclination angle γ is indicated.

Also shown is a CP 432′″ of a system (of which only CP 432′″ is shown)for internal facet metrology of samples, which corresponds to specificembodiments of system 100. In particular, CP 432′″ corresponds tospecific embodiments of CP 132. CP 432′″ includes an external and flatCP first surface 438 a′″, an external and flat CP second surface 438 b″,and an external CP third surface (not numbered). CP second surface 438b′″ is nominally inclined at the nominal inclination angle relative toCP first surface 438 a′″. CP 432′″ is oriented such that CP firstsurface 438 a′″ is parallel to first surface 42 a′″ and CP secondsurface 438 b′″ is nominally parallel to internal facet 44′. Ashape-conforming interface (not shown) may be disposed between the CPthird surface and second surface 42 b″.

When sample 40′″ undergoes inspection, according to the teachingsdisclosed herein, an incident LB is folded by a LFC such as to nominallynormally impinge on CP second surface 438 b″, as described in thedescription of system 100.

FIGS. 5A and 5B schematically depict an optical-based system 500 forvalidating perpendicularity of an internal facet of a sample relative toat least two other external and flat surfaces of the sample, which areparallel to one another, according to some embodiments. System 500corresponds to specific embodiments of system 100. More specifically,each of FIGS. 5A and 5B presents a respective cross-sectional side-viewof system 500 and a sample 50 being inspected by system 500, accordingto some embodiments.

Sample 50 includes an external and flat first surface 52 a, an externalsecond surface 52 b, an external and flat third surface 52 c, and aninternal facet 54. Similarly to internal facet 14 (which constitutes theboundary between, or forms a thin flat layer disposed between, firstpart 16 a and second part 16 b of sample 10), internal facet 54constitutes the boundary between, or forms a thin flat layer disposedbetween, a first part 56 a and a second part 56 b of sample 50. Firstsurface 52 a and third surface 52 c are parallel by design. Further,sample 50 is manufactured to exhibit a (nominal) inclination angle of90° of internal facet 54 relative to first surface 52 a (and thirdsurface 52 c). However, due to fabrication imperfections an actualinclination angle of internal facet 52 b relative to first surface 52 a,labelled in FIGS. 5A and 5B as X′, will generally differ from 90°.

It is noted that using state-of-the-art manufacturing techniques,(manufacturing) tolerances for the actual angle between external, flatsurfaces, which are fabricated to be parallel, are significantly smallerthan tolerances for the actual angle between an internal facet and anexternal, flat surface. Hence, since first surface 52 a and thirdsurface 52 c are manufactured to be parallel, the deviation from theparallelism thereof is expected to be negligible as compared to thedeviation of the actual inclination angle X′ from 90°. Accordingly, anactual angle ψ′ (also referred to as “the actual supplementary angle”)between internal facet 54 and first surface 52 a may be taken to equal180°−X′, i.e. the supplementary angle to the actual inclination angleX′. (The nominal value of the actual supplementary angle ψ′ is 90°.)

System 500 includes a LGA 502 and an ICA 504. LGA 502 corresponds tospecific embodiments of LGA 102 and includes a LFC 522 and a couplinginfrastructure 524, which correspond to specific embodiments of LFC 122and coupling infrastructure 124, respectively. LFC 522 is nominallyconfigured to fold by 90° light incident thereon in a directionperpendicular to the nominal inclination of internal facet 54. Accordingto some embodiments, LFC 522 may be a prism, one or more mirrors, or adiffraction grating. According to some embodiments, LFC 522 may be apentaprism or a like-function prism (i.e. insensitive to variations inpitch) configured to fold light incident thereon by 90°. According tosome embodiments, LFC 522 may be a pair of mirrors set at an angle, or alike-function arrangement of mirrors (i.e. insensitive to variations inpitch), configured to fold light incident thereon by 90°.

According to some embodiments, and as depicted in FIGS. 5A and 5B,coupling infrastructure 524 may include a CP 532 and a shape-conforminginterface 534, which correspond to specific embodiments of CP 132 andshape-conforming interface 134, respectively. CP 532 includes a CP firstsurface 538 a, a CP second surface 538 b, a CP third surface 538 c,which correspond to specific embodiments of CP first surface 138 a, CPsecond surface 138 b, and CP third surface 138 c, respectively. CPsecond surface 538 b is nominally perpendicular to CP first surface 538a. CP 532 further includes a CP fourth surface 538 d, which ispositioned opposite to CP first surface 538 a. According to someembodiments, and as depicted in FIGS. 5A and 5B, CP fourth surface 538 dmay be parallel to CP first surface 538 a.

According to some embodiments, system 500 may further include orientinginfrastructure 540, which corresponds to specific embodiments oforienting infrastructure 140. Orienting infrastructure 540 includes anorientable first stage 542 and an orientable second stage 544, which areconfigured for placement thereon, and orienting of, sample 50 and CP532, respectively, essentially as described with respect to first stage142 and second stage 144 in the description of system 100.

According to some embodiments, and as depicted in FIGS. 5A and 5B,system 500 may further include a controller 508, and, optionally, acomputational module 530, which correspond to specific embodiments ofcontroller 108 and computational module 130, respectively.

ICA 504 corresponds to specific embodiments of ICA 104 and includes alight source 512, a sensor 514, and, optionally, optical equipment 518,which correspond to specific embodiments of light source 112, sensor114, and optical equipment 118, respectively. According to someembodiments, light source 512, sensor 514, and some or all of opticalequipment 518 may constitute components of an autocollimator, which maybe similar to autocollimator 250. According to some embodiments, opticalequipment 518 may include blocking elements (not shown), which may besimilar to blocking elements 256.

ICA 504 is configured to output a first incident LB 505 a directed atsample 50 and second incident LB 505 b is directed at LFC 522. ICA 204and sample 50 are positioned and oriented, such that first incident LB505 a is incident on first surface 52 a perpendicularly thereto. Inoperation, first incident LB 505 a (or at least a portion thereof) isreflected off first surface 52 a—as indicated by a first returned LB 533a. First returned LB 533 a is sensed by sensor 514.

LFC 522 is configured to nominally fold second incident LB 505 b by 90°.More precisely, LFC 522 is configured and oriented to fold secondincident LB 505 b, such that a (first) folded LB 513 b (obtained by thefolding of second incident LB 505 b) is nominally directed at 90°relative to second incident LB 505 b and (nominally) perpendicularly toCP second surface 538 b. In practice, due to manufacturing imperfections(and alignment imprecision in embodiments wherein LFC 522 is sensitiveto variations in pitch), an actual light folding angle X″ of LFC 522 mayslightly deviate from 90°. As elaborated on below, by flipping sample50, so as to invert first surface 52 a and third surface 52 c, andflipping CP 532, so as to invert CP first surface 538 a and CP fourthsurface 538 d, and then repeating the measurement described in the nexttwo paragraphs, the effect of manufacturing imperfections of LFC 522 maybe cancelled out or substantially cancelled out.

In operation, folded LB 513 b, or at least a part thereof, istransmitted into CP 532 via CP second surface 538 b, as indicated by a(first) transmitted LB 517 b. Transmitted LB 517 propagates across CP532, across shape-conforming interface 534, and first part 56 a, andimpinges on internal facet 54 at a (first) incidence angle η₁,essentially as described above with respect to transmitted LB 117 b inthe description of FIG. 1B. The incidence angle η₁ depends on each ofthe deviations ΔX′=90°−X′ (i.e. the deviation from 90° in theinclination of internal facet 54 relative to first surface 52 a),ΔX″=90°−X″ (i.e. the deviation of the (actual) light folding angle ofLFC 522 from 90°), and ΔX′″=90°−X′″ (i.e. the deviation from 90° in theinclination of CP second surface 538 b relative to CP first surface 538a). In particular, system 500 is nominally configured to havetransmitted LB 517 b normally impinge on internal facet 54 when ΔX′=0. Anormal to internal facet 54 is indicated in FIG. 5A by a (straight)dashed line C₁.

A transmitted LB 517 b (or at least a portion thereof) is specularlyreflected off internal facet 54 (i.e. at a return angle equal to minusthe first incidence angle η₁), as indicated by a (first) reflected LB521 b. Reflected LB 521 b travels back towards LFC 522 via first part 56a, shape-conforming interface 534, and CP 532. A (first) emerged LB 525b indicates a (first) portion of reflected LB 521 b, which is refractedto the outside CP 532 via CP second surface 538 b (unless exactlyperpendicularly incident on CP second surface 538, in which case thefirst portion will maintain the propagation direction thereof; a secondportion of reflected LB 521 b, specularly reflected by CP second surface538 b inside CP 532, is not shown). Emerged LB 525 b is folded by LFC522 at the light folding angle X″, as indicated by a second returned LB533 b. Second returned LB 533 b is sensed by sensor 514.

An angle δ₁between second returned LB 533 b and first returned LB 533a—also referred to as “the first angular deviation”—depends on thedeviations ΔX′, ΔX″, and ΔX′″, and a refractive index n′ of first part56 a (which is equal to, or close to, the refractive indices of CP 532and shape-conforming interface 534). FIG. 5C schematically depicts afirst spot 547 a and a second spot 547 b formed by first returned LB 533a and second returned LB 533 b, respectively, on a photosensitivesurface 548 of sensor 514, according to some embodiments. w₁ and w₂ arethe horizontal coordinates (i.e. as measured along the x-axis) of firstspot 547 a and second spot 547 b, respectively. The angle δ₁ may bedirectly inferred from the difference Δw=w₂−w₁.

Referring to FIG. 5B, as compared to FIG. 5A, sample 50 has beenflipped, such that first surface 52 a and third surface 52 c areinverted (while maintaining the nominal orientation of internal facet 54relative to LGA 502) and CP 532 has been flipped, such that CP firstsurface 538 a and CP fourth surface 538 d are inverted (whilemaintaining a nominal orientation of CP second surface 538 b relative tosample 50).

In operation, third incident LB 505 a′ is directed at sample 50,perpendicularly thereto, and fourth incident LB 505 b′ is directed atLFC 522. Third incident LB 505 a′ (or at least a portion thereof) isreflected off third surface 52 c—as indicated by a third returned LB 533a′. Third returned LB 533 a′ is sensed by sensor 514.

Fourth incident LB 505 b′ impinges on LFC 522, resulting in a secondfolded LB 513 b′, which in turn impinges on CP second surface 538 b,resulting in a second transmitted LB 517 b′, which propagates across CP532, across shape-conforming interface 534, and into first part 56 a ofsample 50. Second transmitted LB 517 b′ impinges on internal facet 54 ata second incidence angle 112. The second incidence angle η₂ depends oneach of the deviations Δψ′=90°−ψ′ (i.e. the deviation from 90° in theinclination of internal facet 54 relative to third surface 52 c),ΔX″=90°−X″, and ΔX′″=90°−X′″ (implicitly assuming that the uncertaintyin the parallelism of the CP first surface 538 a and CP fourth surface538 d is smaller than a required measurement precision of the actualinclination angle X′). A normal to internal facet 54 is indicated inFIG. 5B by a (straight) dashed line C₂.

Second transmitted LB 517 b′ is (at least in part) specularly reflectedoff internal facet 54 (i.e. at a return angle ζ equal to minus thesecond incidence angle η₂), as indicated by a second reflected LB 521b′. Second reflected LB 521 b′ travels back towards LFC 522 via firstpart 56 a, shape-conforming interface 534, and CP 532. A second emergedLB 525 b′ indicates a portion of second reflected LB 521 b′, which exitsCP 532 via CP second surface 538 b (a portion of second reflected LB 521b′, internally reflected by CP second surface 538 b, is not shown).Second emerged LB 525 b′ is folded by LFC 522 at the light folding angleX″, as indicated by a fourth returned LB 533 b′. Fourth returned LB 533b′ is sensed by sensor 514.

An angle δ₂ between fourth returned LB 533 b′ and third returned LB 533a′—also referred to as “the second angular deviation”—depends on thedeviations ΔX′, ΔX″, and ΔX′″, and the refractive index n′. Morespecifically, angle δ₂ exhibits the same dependence on ΔX′=180°−ΔX′,ΔX″, and Δψ′″=180°−ΔX′″, and the refractive index n′, as exhibited bythe angle δ₁ on the deviations ΔX′, ΔX″, and ΔX′″, and the refractiveindex n′, respectively. FIG. 5D schematically depicts a third spot 547a′ and a fourth spot 547 b′ formed by third returned LB 533 a′ andfourth returned LB 533 b′, respectively, on photosensitive surface 548,according to some embodiments. w₁′ and w₂′ are the horizontalcoordinates of third spot 547 a′ and fourth spot 547 b′, respectively.The angle δ₂ may be directly inferred from the difference Δw′=w₂′−w₂′.

While in FIGS. 5C and 5D Δw and Δw′ are both shown as being negative (sothat δ₁ and δ₂ are both negative), it is to be understood that generallyΔw and Δw′ may have opposite signs (so that δ₁ and δ₂ will have oppositesigns), or may both be positive (so that δ₁ and δ₂ are both positive).

Each of the measured angles δ₁ and δ₂ may be used to provide arespective estimate of the deviation angle ΔX′. Absent any imperfectionsin system 500, η₂ would equal −η₁ and δ₁ would equal −δ₂. However, inpractice, the two estimates will generally differ due to the actuallight folding angle deviating from 90° and the actual inclination angleof CP second surface 538 b deviating from 90°. Since δ₁ and δ₂ have thesame (when the LFC is insensitive to variations in pitch), orsubstantially the same, dependence on the deviation ΔX″ (i.e. both δ₁and δ₂ increase as X″ is increased and decrease as X″ is decreased), thedeviation from 90° of the (actual) light folding angle may be cancelledout, or substantially cancelled out, by averaging over the two estimatesof the deviation angle ΔX′. Denoting by <X′> the so-averaged estimate ofthe actual inclination of internal facet 54, and by <ΔX′> the averagedestimate of the deviation of the actual inclination angle from 90° (i.e.<X′>=90°−<′X′>), <X′> can be shown to equal90°+(δ₁−δ₂)/(4n′)+ΔX′″·(n′−1)/n′. More generally, <X′> may be between90°+0.95·[(δ₁−δ₂)/(4n)+ΔX′″·(n−1)/n)] and90°+1.05·[(δ₁−δ₂)/(4n)+ΔX′″·(n−1)/n)], between90°+0.9·[(δ₁−δ₂)/(4n)+ΔX′″·(n−1)/n)] and90°+1.1·[(δ₁−δ₂)/(4n)+ΔX′″·(n−1)/n)], or even between90°+0.8·[(δ₁−δ₂)/(4n)+ΔX′″·(n−1)/n)] and90°+1.2·[(δ₁−δ₂)/(4n)+ΔX′″·(n−1)/n)]. Each possibility corresponds toseparate embodiments. In particular, in embodiments wherein ICA 504 isor includes an autocollimator, <X′> can be shown to equal, or to equalabout, 90°+(Δw−Δw′)/(2·f₀·n′)+ΔX′″(n′−1)/n′, wherein f₀ is the focallength of the collimating lens of the autocollimator.

According to some alternative embodiments, not depicted in FIGS. 5A and5B, light source 512 and optical equipment 518 may be configured toproduce an expanded (collimated) laser beam or a pair of parallel andspaced-apart (collimated) laser beams, essentially as described above inthe description of system 100. According to still other embodiments, ICA504 may be or includes an interferometric setup, as described above inthe description of system 100.

While in each of FIGS. 1A, 1B, 2, 3, 5A, and 5B the samples are shown asincluding a single internal facet (e.g. internal facet 14 in sample 10and internal facet 54 in sample 50), the disclosed systems may also beutilized to obtain information about a plurality of internal facets,which are nominally parallel. According to some embodiments, theinformation may be collective information and may specify the average(mean) actual inclination angle of the internal facets, or a weightedaverage of the actual inclination angles, as described below.

Referring to FIG. 6A, FIG. 6A depicts such a sample, a sample 60,according to some embodiments. To facilitate the description, byrendering it more concrete, sample 60 is shown as including twonominally parallel internal facets, but the skilled person will readilyappreciate that it is straightforward to apply the teachings of FIGS. 6Aand 6B to samples including three or more internal facets, which arenominally parallel. Sample 60 includes an external, flat first surface62 a, an external second surface 62 b, a first internal facet 64 a, anda second internal facet 64 b. Second surface 62 b is set at an anglerelative to first surface 62 a (and may or may not be flat). Firstinternal facet 64 a is flat and nominally inclined at a nominalinclination angle (not indicated) relative to first surface 62 a. Secondinternal facet 64 b is flat and nominally parallel to first internalfacet 64 a. First internal facet 64 a is positioned between secondsurface 62 b and second internal facet 64 b. A first part 66 a of sample60 is partially bounded by second surface 62 b and first internal facet64 a. A second part 66 b of sample 60 is partially bounded by firstinternal facet 64 a and second internal facet 64 b. Second internalfacet 64 b extends between second part 66 b and a third part 66 c ofsample 60. First part 66 a and second part 66 b have the same refractiveindex (or close refractive indices). First internal facet 64 aconstitutes a thin layer of material(s) characterized by a refractiveindex, which differs from that of first part 66 a and second part 66 b.

Information regarding the actual inclination angles of first internalfacet 64 a and second internal facet 64 b relative to first surface 62 amay be obtained utilizing any one of systems 100, 200, or 300,essentially as described above in the corresponding descriptions andwith additions/adjustments as specified below. In embodiments whereinthe nominal inclination angle is 90° and sample 60 includes an external,flat third surface 62 c, which is parallel to first surface 62 a,information regarding the actual inclination angles may be obtainedutilizing system 500, essentially as described above in thecorresponding descriptions and with additions/adjustments as specifiedbelow.

To facilitate the description and render the discussion more concrete,it is assumed that a system (not shown in FIG. 6A), which corresponds tospecific embodiments of system 100, is utilized to inspect sample 60.Indicated is a first incident LB 605 a (only a single ray thereof isshown), which is projected on first surface 62 a, perpendicularlythereto. A first returned LB 633 a is obtained from the reflection offirst incident LB 605 a off first surface 62 a. Also indicated is atransmitted LB 617 b (only a single ray thereof is shown), which may beobtained by nominally folding (using a LFC of the system (not shown)employed to perform the inspection) a second incident LB at the nominalinclination angle, which is then transmitted into a CP of the system,oriented such that the folded LB is nominally perpendicularly incidenton an external, flat surface of the CP, which is nominally parallel tointernal facets 64. Transmitted LB 617 b exits the CP into ashape-conforming interface positioned between the CP and sample 60. Eachof the CP and the shape-conforming interface are characterized by arefractive index equal to, or at least close to, that of first part 66 aand second part 66 b of sample 60. Transmitted LB 617 b enters sample 60via second surface 62 b. Transmitted LB 617 b nominally perpendicularlyimpinges on first internal facet 64 a. A reflected LB 621 b correspondsto the portion of transmitted LB 617 b, which is specularly reflectedoff first internal facet 64 a. A (first) transmitted portion 637 bcorresponds to the portion of transmitted LB 617 b, which is transmittedinto second part 66 b. Transmitted portion 637 b nominallyperpendicularly impinges on second internal facet 64 b. A reflectedportion 641 b corresponds to the portion of transmitted portion 637 b,which is specularly reflected off second facet 64 b. A secondtransmitted portion 645 b indicates the portion of reflected portion 641b, which is transmitted back into first part 66 a via first internalfacet 64 a.

FIG. 6B schematically depicts a first spot 647 a and a pair of spots 647b—including a second spot 647 b 1 and a third spot 647 b 2—on aphotosensitive surface 648 of a sensor 614 of the system employed toinspect sample 60, according to some embodiments. First spot 647 a isformed by first returned LB 633 a. Second spot 647 b 1 and a third spot647 b 2 are formed by the returned LBs induced by reflected LB 621 b andsecond transmitted portion 645 b (i.e. by reflection off first internalfacet 64 a and second internal facet 64 b, respectively). Utilizingblocking elements and blocking/filtering techniques, first returned LB633 a may be discriminated from the returned LBs (not shown) induced byreflected LB 621 b and second transmitted portion 645 b. If second spot647 b 1 (and third spot 647 b 2) cannot be attributed to one of the tworeturned LBs, induced by reflected LB 621 b and second transmittedportion 645 b, then only collective information (e.g. average actualinclination) about first internal facet 64 a and second internal facet64 b may be extracted from the positions of second spot 647 b 1 andthird spot 647 b 2 (from the average of the deviation angles of thereturned LBs, associated with reflected LB 621 b and second transmittedportion 645 b, relative to first returned LB 633 a).

According to some embodiments, the intensity of the returned LB,associated with reflected LB 621b, may be significantly greater than theintensity of the returned LB, associated with second transmitted portion645 b. Accordingly, first spot 647 b 1 may be attributed to reflected LB621 b or second transmitted portion 645 b according to whether thebrightness thereof is respectively greater or lesser than that of secondspot 647 b 2 (with the inverse applying for second spot 647 b 2).

According to some embodiments, first internal facet 64 a is configuredto reflect light at a first spectrum and second internal facet 64 b isconfigured to reflect light at a second spectrum. The second spectrumsufficiently differs from the first spectrum so as to allowdiscriminating between the returned LB induced by reflection off firstinternal facet 64 a, and the returned LB induced by the reflection offsecond internal facet 64 b. The discrimination may be carried oututilizing a spectral filter, which is configured to selectively filtertherethrough light in either of the first and second spectra, asdescribed above in the description of FIGS. 1A and 2 . Discriminationbetween first returned LB 633 a and the returned LBs, induced byreflection off internal facets 64, may be similarly carried out.

According to some embodiments, wherein sample 60 includes third surface62 c, which is opposite to first surface 62 a, additional collective orindividual information regarding the actual inclination angles ofinternal facets 64 may be obtained by flipping sample 60, such that thefirst surface 62 a and third surface 62 c are inverted and anorientation of second surface 62 b relative to the LGA, used inperforming the measurements, is maintained, and repeating themeasurement, essentially as taught above in the description of system500 and below in the description of the method of FIGS. 8A and 8B.

Methods

According to an aspect of some embodiments, there is provided anoptical-based method for metrology of internal facets of samples. Themethod may be employed to validate an orientation of one or moreinternal facets of a sample relative to an external and flat surface ofthe sample. FIG. 7 presents a flowchart of such a method, anoptical-based method 700, according to some embodiments. Method 700 mayinclude:

-   -   An optional stage 705, wherein the system (e.g. system 100) used        to implement the method is calibrated.    -   A stage 710, wherein a sample (e.g. sample 10), which is to be        tested, is provided. The sample includes an external, flat first        surface (a first external surface, which is flat; e.g. first        surface 12 a) and an internal facet (e.g. internal facet 14)        nominally inclined at a nominal inclination angle (e.g. the        nominal inclination angle α) relative to the first surface.    -   A stage 720, wherein a pair of parallel light beams (LBs) are        generated (e.g. by light source 112 and optical equipment 118 or        by autocollimator 250): A first incident LB (e.g. first incident        LB 105 a) is projected on the first surface of the sample        perpendicularly thereto. A second incident LB (e.g. second        incident LB 105 b) is projected on a light guiding arrangement        (LGA; e.g. LGA 102) in parallel to the first incident LB.    -   A stage 730, wherein a first returned LB (e.g. first returned LB        133 a) is obtained from a reflection of the first incident LB        off the first surface of the sample.    -   A stage 740, wherein a second returned LB (e.g. second returned        LB 133 b) is obtained by redirection by the LGA of the second        incident LB into or onto the sample, reflection thereof off the        internal facet after nominally normally impinging on the        internal facet, and inverse redirection by the LGA.    -   A stage 750, wherein an angular deviation of the second returned        LB relative to the first returned LB is measured by sensing the        first returned LB and the second returned LB (e.g. by sensor 114        or autocollimator 250).    -   A stage 760, wherein an actual inclination angle (e.g. the        actual inclination angle α′) of the internal facet relative to        the first surface is deduced based at least on the measured        angular deviation.

As used herein, the term “obtaining” may be employed both in an activeand a passive sense. Thus, for example, in stage 730 the first returnedLB may be obtained not due to any operation implemented in stage 730 butrather due to the generation of the first incident LB in stage 720.Generally, a stage may describe an active operation performed by a useror by the system used to implement the method, and/or the results oreffects of one or more operations performed in one or more earlierstages. Method 700 may be implemented employing an optical-based system,such as any one of optical-based systems 100, 200, and 300 oroptical-based systems similar thereto, as described above in therespective descriptions thereof. In particular, according to someembodiments, method 700 may be autocollimator-based, based on themeasurement of distance between laser beams, or may be based oninterferometry, as detailed in the description of the variousembodiments of system 100. In stage 730, the second incident LB may benominally folded at the nominal inclination angle utilizing any one ofLFC 122, LFC 222, and prism 322, or a similar function LFC. Similarly,the second returned LB may be obtained utilizing any one of LFC 122, LFC222, and prism 322, or a like-function LFC. According to someembodiments, the internal facet may demarcate a flat boundary between afirst part (e.g. first part 16 a) and a second part (e.g. second part 16b) of the sample, which differ in their refractive indices.Alternatively, according to some embodiments, the internal facet mayconstitute a thin and flat and layer between a first part and a secondpart of the sample, which has a different refractive index than each ofthe first part and the second part (whose refractive indices may or maynot be the same). The first part may extend between the internal facetand an external, flat second surface (e.g. second surface 12 b) of thesample. In stage 740, a transmitted LB (e.g. transmitted LB 117 b),which constitutes a portion of second incident LB transmitted into thesample, may enter thereinto via the second surface.

According to some embodiments, in stage 720 a collimated light beam,such as LB 201, may be generated, of which a first sub-beam and a secondsub-beam constitute the first incident LB and the second incident LB,respectively. According to some embodiments, the first incident LB andthe second incident LB may be adjacent. According to some embodiments,the first incident LB and the second incident LB may form complementaryportions of the collimated light beam. Alternatively, according to someembodiments, the first incident LB and the second incident LB may bespaced apart, with a portion of the collimated light beam, which wouldhave been positioned therebetween, having been removed (e.g. blocked,for example, using a light absorbing filter or an opaque plate).According to some embodiments, the collimated light beam may begenerated using an autocollimator, such as autocollimator 250.

According to some embodiments, the LFC may be configured such that thelight folding angle thereof is independent of a pitch angle at which theLFC is set (so that the second incident LB is nominally folded at thenominal inclination angle a irrespectively of the pitch angle).According to some such embodiments, the LFC may be a pentaprism or alike-function prism, or a pair of plane mirrors set at an angle relativeto one another, or a like-function mirror arrangement, as describedabove in the Systems subsection in the description of systems 100 and300.

According to some embodiments, the LGA may include, in addition to theLFC, a coupling infrastructure, such as coupling infrastructure 124. Thecoupling infrastructure is configured to guide light, nominally foldedby the LFC (e.g. folded LB 113 b) at the nominal inclination angle, intoor onto to the sample, so that the transmitted light (e.g. transmittedLB 117 b) nominally normally impinges on the internal facet.

According to some embodiments, the coupling infrastructure may include acoupling prism (CP), such as CP 132, and a shape-conforming interface,such as shape-conforming interface 134. Each of the CP and theshape-conforming interface may be characterized by refractive indicesequal to, or close to equal to, the refractive index of the sample or atleast the first part of the sample in embodiments wherein the first partand second part of the sample do not have the same refractive index. TheCP includes an external and flat first surface (referred to as “CP firstsurface”), an external and flat second surface (referred to as “CPsecond surface”), and an external third surface (referred to as “CPthird surface”), such as CP first surface 138 a, CP second surface 138b, and CP third surface 138 c, respectively. In particular, the CPsecond surface is nominally inclined at the nominal inclination angle arelative to the CP first surface.

The shape-conforming interface is disposed between the CP and the firstpart of the sample, adjacently to each, so as to define a continuum ofmaterials having equal, or close to equal, refractive indices. Morespecifically, the shape-conforming interface is disposed between the CPthird surface and the second surface of the sample with the CP and thesample being mutually aligned, such that the CP second surface and theinternal facet of the sample are nominally parallel.

The forming of a continuum of materials having the same refractiveindices, or close refractive indices, helps ensure that in stage 740 (i)the propagation direction of a light beam transmitted into the CP (e.g.transmitted LB 117 b) is maintained on crossing from the CP into theshape-conforming interface, and, next, on crossing from theshape-conforming interface into the first part of the sample, and (ii)the propagation direction of the light beam reflected off the internalfacet (e.g. reflected LB 121 b) is maintained on crossing from the firstpart of the sample into the shape-conforming interface, and, next, oncrossing from the shape-conforming interface into the CP.Advantageously, this helps ensure that a transmitted portion (e.g.transmitted LB 117 b) of a light beam (e.g. folded LB 113 b), which isnormally incident on the CP second surface, will nominally normallyimpinge on the internal facet of the sample.

Thus, in embodiments including both the CP and shape-conforminginterface, a folded LB (e.g. folded LB 113 b)—obtained by the folding ofthe second incident LB by the LFC—impinges on the CP second surfacenominally normally thereto and is (at least in part) transmitted intothe CP. The transmitted LB (e.g. transmitted LB 117 b) continuouslytravels across the CP, across the shape-conforming interface, and thefirst part of the sample. The transmitted LB nominally normally impingeson the internal facet and is reflected (at least in part) off theinternal facet. The reflected LB (e.g. reflected LB 121 b) travels backacross the first part, the shape-conforming interface, and the CP. Atleast a portion (e.g. emerged LB 125 b) of the reflected LB emerges fromthe CP in the direction of the LFC. The LFC nominally folds the emergedLB at the nominal inclination angle, thereby obtaining the secondreturned LB.

According to some embodiments, in stage 705, an additional incident LB(e.g. additional incident LB 205 s) may be projected nominally normallyto the CP first surface. The additional incident LB may be used tovalidate that the CP first surface and the first surface of the sampleare aligned, for example, by measuring an angular deviation between anadditional returned LB (e.g. additional returned LB 233 s), obtainedfrom the reflection of the additional incident LB off the CP firstsurface, and first returned LB.

According to some embodiments, in stage 705, “gold standard” (GS)samples may be employed as part of the calibration of the system used toimplement method 700. More specifically, given a sample to be tested, acorresponding GS sample (i.e. a sample that is known to exhibit therequisite geometry to high precision and has the same refractive indexas the sample to be tested) may be employed in calibrating the system.The GS sample may be employed to calibrate an orienting infrastructure(e.g. orienting infrastructure 140, orienting infrastructure 240) andthe LGA, such that (i) the first incident will normally impinge on afirst surface (analogous to first surface 12 a) of the GS sample and(ii) the transmitted LB will (i.e. to a precision afforded by the GSsample and the LGA) perpendicularly impinge on an internal facet(analogous to internal facet 14) of the GS sample.

According to some embodiments, a (first) orientable stage (e.g. stage142), on which the sample may be mounted, may be used to orient the GSsample relative to each of the LGA, as a whole or relative a singlecomponent thereof (for example, the CP), and the ICA. Additionally, oralternatively, a second orientable stage (e.g. second stage 144) may beused to orient the CP relative to the GS sample and the LFC. Anautocollimator, whether part of the ICA (in embodiments wherein thesystem includes an autocollimator), or not included in the system, maybe used to validate the perpendicularity of the transmitted LB.

According to some embodiments, calibration or additional calibration maybe performed after stage 710, once the sample to be tested has beenprovided and disposed e.g. on the orientable stage. The additionalcalibration may include, for example, orienting or re-orienting theorientable stage, on which the sample to be tested is mounted, such thatthe first incident LB perpendicularly impinges on the first surface ofthe sample to be tested. According to some embodiments, in stage 750 anautocollimator (e.g. autocollimator 250, and, more generally, inembodiments wherein an autocollimator is used in preparing the incidentLBs, that same autocollimator) may be employed to sense the first andsecond returned LBs (e.g. the striking locations thereof on aphotosensitive surface of a sensor of the autocollimator), and therebymeasured the angular deviation. According to some embodiments, blockingelements, such as shutters and/or spectral filters may be employed toselectively block (or at least partially block) each of the returnedLBs, essentially as described above in the description of systems 100and 200. Beyond facilitating the attribution of each of a pair of spots(on a photosensitive surface of a light or image sensor (e.g. sensor114) utilized to sense the returned LBs) to the returned LB, which hasformed the spot, the blocking of one returned LB, while sensing theother returned LB, may serve to increase measurement precision byattenuating the signal associated with stray light.

According to some embodiments, particularly embodiments wherein stages710, 720, and 730 are implemented employing an autocollimator, such asautocollimator 250, in stage 740, the angular deviation {tilde over (δ)}of the second returned LB relative to the first returned LB may becomputed via {tilde over (δ)}=(ũ₂−ũ₁)/{tilde over (f)}. ũ₁ and ũ₂ arethe horizontal coordinates of a first spot (e.g. first spot 247 a) and asecond spot formed (e.g. second spot 247 b) on the photosensitivesurface (e.g. photosensitive surface 248) of the autocollimator by thefirst returned LB and the second returned LB, respectively. {tilde over(f)} is the focal length of a collimating lens of the autocollimator.

In stage 750, the actual inclination angle {tilde over (α)}′ may becomputed using the laws of geometrical optics and, in particular,Snell's law (and taking into account the actual light folding angle ofthe LFC, the actual inclination angle of the CP second surface relativeto the CP first surface, and the value of refractive index of the firstpart of the sample).

According to some embodiments, wherein the sample (e.g. sample 60)includes a plurality of internal facets (e.g. internal facets 64),nominally perpendicular to the first surface, and, except for theinternal facets, the sample is further characterized by a uniform orclose to uniform refractive index, in stage 740, a plurality of returnedLBs is obtained by redirection by the LGA of the second incident LB intoor onto the sample, reflection thereof off each of the internal facets,and inverse redirection by the LGA, essentially as described in thedescription of FIGS. 6A and 6B. In stage 750, a plurality of angulardeviations of each of the plurality of returned LB s relative to thefirst returned LB is measured by sensing the first returned LB and eachof the plurality of returned LBs. According to some such embodiments, instage 760, actual inclination angles of each of the plurality ofinternal facets relative to the first surface may be deduced based atleast on the plurality of measured angular deviations. According to someembodiments, each of the spots, formed by the plurality of returned LBson a photosensitive surface of a sensor (e.g. sensor 614), may beattributed to a respective one of the plurality of returned LBs based onrelative brightness of the spots, and/or—in embodiments wherein each ofthe internal facets is configured to reflect light at a respectivedistinct spectrum—employing spectral filters. Additionally, oralternatively, according to some embodiments, collective informationregarding the actual inclination angles (such as the mean actualinclination angle) is deduced based at least on the plurality ofmeasured angular deviations.

FIGS. 8A and 8B present a flowchart of an optical-based method 800 formetrology of internal facets of samples, according to some embodiments.Method 800 corresponds to specific embodiments of method 700 and may beemployed to validate perpendicularity of one or more internal facets ofa sample relative to at least two external and flat surfaces of thesample, which are parallel to one another. Method 800 may include:

-   -   A stage 805, wherein a sample (e.g. sample 50) to be tested is        provided. The sample includes an external, flat first surface        (i.e. a first external surface, which is flat; e.g. first        surface 52 a), an external second surface (i.e. a second        external, which may or may not be flat; e.g. second surface 52        b), an external, flat third surface (i.e. a third external        surface, which is flat; e.g. third surface 52 c) parallel to the        first surface, and an internal facet nominally inclined at 90°        relative to the first surface.    -   A stage 810, wherein a first pair of parallel LBs are generated        (e.g. by light source 512, and, optionally, optical equipment        518): A first incident LB (e.g. first incident LB 505 a) is        projected on the first surface of the sample perpendicularly        thereto. A second incident LB (e.g. second incident LB 505 b) is        projected on the LGA (in parallel to the first incident LB).    -   A stage 815, wherein a first returned LB (e.g. first returned LB        533 a) is obtained from a reflection of the first incident LB        off the first surface.    -   A stage 820, wherein a second returned LB (e.g. second returned        LB 533 b) is obtained by redirection by the LGA of the second        incident LB into or onto the sample, reflection thereof off the        internal facet after nominally normally impinging on the        internal facet, and inverse redirection by the LGA.    -   A stage 825, wherein a (first) angular deviation of the second        returned LB relative to the first returned LB is measured by        sensing the first returned LB and the second returned LB (e.g.        by sensor 514).    -   A stage 830, wherein the sample is flipped, so as to invert the        first and third surfaces (while maintaining a nominal        orientation of the internal facet relative to the LGA).    -   A stage 835, wherein a second pair of parallel LBs are generated        (e.g. by light source 512 and, optionally, optical equipment        518): A third incident LB (e.g. third incident LB 505 a′) is        projected on the third surface of the sample perpendicularly        thereto. A fourth incident LB (e.g. fourth incident LB 505 b′)        is projected on the LGA (in parallel to the third incident LB).    -   A stage 840, wherein a third returned LB (e.g. third returned LB        533 a′) is obtained from a reflection of the third incident LB        off the third surface.    -   A stage 845, wherein a fourth returned LB (e.g. fourth returned        LB 533 b′) is obtained by redirection by the LGA of the fourth        incident LB into or onto the sample, reflection thereof off the        internal facet after nominally normally impinging on the        internal facet, and inverse redirection by the LGA.    -   A stage 850, wherein a (second) angular deviation of the fourth        returned LB relative to the third returned LB is measured by        sensing the third returned LB and the fourth returned LB (e.g.        by sensor 514).    -   A stage 855, wherein an actual inclination angle of the internal        facet relative to the first surface is deduced based on the        measured angular deviations.

Method 800 may be implemented employing an optical-based system, such asoptical-based system 500 or an optical-based system similar thereto, asdescribed above in the description of FIGS. 5A-5D. In particular,according to some embodiments, method 800 may be autocollimator-based,based on the measurement of distance between laser beams, or based oninterferometry. In stage 820, the first folded LB and the secondreturned LB may be obtained from the second incident LB and the firstreflected LB, respectively, utilizing a LFC configured to nominally foldby 90° light incident thereon, such as LFC 522 or a like-function LFC.According to some embodiments, the LFC may be or include a prism (e.g. apentaprism) configured to fold light by 90°, or one or more mirrors(jointly) configured to fold light by 90° Similarly, in stage 845, thesecond folded LB and the fourth returned LB may be obtained from thefourth incident LB and the second reflected LB, respectively, utilizingLFC 522 or a like-function LFC.

According to some embodiments, the LGA may include, in addition to theLFC, a coupling infrastructure, such as coupling infrastructure 524. Thecoupling infrastructure is configured to guide light, folded by the LFC(e.g. folded LB 513 b), into or onto to the sample, so that thetransmitted light (e.g. transmitted LB 517 b) nominally normallyimpinges on the internal facet.

According to some embodiments, the coupling infrastructure may include acoupling prism (CP), such as CP 532, and a shape-conforming interface,such as shape-conforming interface 534. Each of the CP and theshape-conforming interface are characterized by a respective refractiveindex equal to, or close to equal to, that of the sample or at least thefirst part of the sample in embodiments wherein the first part andsecond part of the sample do not have the same refractive index. The CPincludes an external and flat first surface (referred to as “CP firstsurface”), an external and flat second surface (referred to as “CPsecond surface”), and an external third surface (referred to as “CPthird surface”), such as CP first surface 538 a, CP second surface 538b, and CP third surface 538 c, respectively. In particular, the CPsecond surface is nominally perpendicularly inclined relative to the CPfirst surface. The CP and shape-conforming interface may be utilizedessentially as described above in the description of method 700, and,optionally, additionally utilized as described below.

According to some embodiments, the CP includes an external and flatfourth surface (referred to “CP fourth surface”), such as CP fourthsurface 538 d. The CP fourth surface is opposite and parallel to the CPfirst surface. In such embodiments, in stage 830, the CP may also beflipped, such that the CP first surface and the CP fourth surface, witha nominal orientation of the CP second surface (through which the light,folded by the LFC, enters into the CP) relative to the internal facetbeing maintained. According to some embodiments, in stages 810 and 835,an autocollimator (e.g. autocollimator) may be used to generate thepairs of parallel incident LBs. According to some embodiments, in stages815, 820, 840, and 845 an autocollimator (e.g. the autocollimator usedin preparing the incident LBs) may be employed to sense the returnedLBs. According to some embodiments, shutters and/or spectral filters maybe employed to selectively block (or at least partially block) one ofthe second returned LB and the first returned LB, and one of the fourthreturned LB and the third returned LB, essentially as described above inthe description of FIGS. 5A and 5B.

According to some embodiments, method 800 may include an optionalcalibration stage (not shown in FIGS. 8A and 8B) similar to stage 705 ofmethod 700, and which is (partially) repeated after flipping the samplein stage 830 (and performed before stages 835 to 855). Morespecifically, in stage 830, after the sample is flipped, the orientationof the sample may be reoriented, such that light transmitted into thesample is incident on the internal facet nominally perpendicularlythereto. In embodiments, wherein the CP is also flipped, the CP may alsobe reoriented, such that light folded by the LFC (e.g. second folded LB513 b′) will nominally perpendicularly impinge on the CP second surface.

According to some embodiments, particularly embodiments wherein stages810, 815, 820, 835, 840, and 845 are implemented employing anautocollimator (such as autocollimator 250), in stage 825, the firstangular deviation δ₁ of the second returned LB relative to the firstreturned LB is obtained via {tilde over (δ)}₁=({tilde over (w)}₂−{tildeover (w)}₁)/{tilde over (f)}₀. {tilde over (w)}₁ and {tilde over (w)}₂are the horizontal coordinates of a first spot and a second spot (e.g.first spot 547 a and second spot 547 b) formed on the photosensitivesurface (e.g. photosensitive surface 548) of the autocollimator by thefirst returned LB and the second returned LB, respectively. {tilde over(f)}₀ is the focal length of a collimating lens of the autocollimator.Similarly, in stage 850, the second angular deviation {tilde over (δ)}₂of the fourth returned LB relative to the third returned LB is obtainedvia {tilde over (δ)}₁=({tilde over (w)}₂′−{tilde over (w)}₁′)/{tildeover (f)}₀. {tilde over (w)}₁′ and {tilde over (w)}₂′ are the horizontalcoordinates of a third spot and a fourth spot (e.g. third spot 547 a′and fourth spot 547 b′) formed on the photosensitive surface of theautocollimator by the third returned LB and the fourth returned LB,respectively.

In stage 855, the value of the actual inclination angle {tilde over(X)}′ (or more precisely, the average value obtained from averaging overthe two obtained estimates) may obtained from the (measured values ofthe) angular deviations {tilde over (δ)}₁ and {tilde over (δ)}₂ via therelation

{tilde over (X)}′

=90°−

Δ{tilde over (X)}′

={tilde over (X)}+({tilde over (δ)}₁′−{tilde over (δ)}₂)/(4ñ′)+Δ{tildeover (X)}′″·(ñ′−1)ñ′. ñ′ is the refractive index of the first part ofthe sample (as well as the CP and the shape-conforming interface or isat least close to the respective refractive indices thereof).

According to some embodiments, wherein the sample (e.g. sample 60)includes a plurality of internal facets (e.g. internal facets 64),nominally perpendicular to the first surface, and, except for theinternal facets, the sample is further characterized by a uniform orclose to uniform refractive index, in stage 820, a first plurality ofreturned LBs is obtained by redirection by the LGA of the secondincident LB into or onto the sample, reflection thereof off each of theinternal facets, and inverse redirection by the LGA, essentially asdescribed in the description of FIGS. 6A and 6B. In stage 825, a firstplurality of angular deviations of each of the first plurality ofreturned LBs relative to the first returned LB is measured by sensingthe first returned LB and each of the first plurality of returned LBs.Similarly, in stage 845, a second plurality of returned LBs is obtainedby redirection by the LGA of the fourth incident LB into or onto thesample, reflection thereof off each of the internal facets, and inverseredirection by the LGA. In stage 850, a second plurality of angulardeviations of each of the second plurality of returned LBs relative tothe third returned LB is measured by sensing the third returned LB andeach of the second plurality of returned LBs. According to some suchembodiments, in stage 855, actual inclination angles of each of theplurality of internal facets relative to the first surface may bededuced based on the first plurality of measured angular deviations andthe second plurality of measured angular deviations. According to someembodiments, each of the spots formed by the plurality of returned LBsmay be attributed to a respective one of the plurality of returned LBsbased on relative brightness of the spots, and/or—in embodiments whereineach of the internal facets is configured to reflect light at arespective distinct spectrum—employing spectral filters. Additionally,or alternatively, according to some embodiments, collective informationregarding the actual inclination angles (such as the mean actualinclination angle) is deduced based at on the first and secondpluralities of measured angular deviations.

According to some embodiments, wherein when the sample is flipped, suchthat the first and third surfaces thereof are inverted, and such thatorientation of the internal facet relative to the LGA is maintained,and, in addition, the internal facet remains nominally parallel to theCP second surface (when the CP is not flipped), then method 800 mayadditionally include four measurements instead: a first measurement withboth the sample and the CP unflipped, a second measurement with thesample unflipped and the CP flipped, a third measurement with both thesample and the CP flipped, and a fourth measurement with the sampleflipped and the CP unflipped. The four measurements may increasemeasurement precession by effectively canceling out the contribution ofΔ{tilde over (X)}′″ to

{tilde over (X)}′

. A non-limiting example of such a sample, is sample 40 in FIG. 4A,according to some specific embodiments thereof wherein sample 40 furthercomprises an external and flat surface opposite to first surface 42 a.

Additional Systems

FIG. 9 schematically depicts an optical-based system 900 for internalfacet metrology of samples, according to some embodiments, System 900 issimilar to system 100 but unlike some embodiments of system 100, doesnot include any coupling infrastructure (such as coupling infrastructure124). System 900 is configured for use with samples including at leasttwo external and flat surfaces and an internal facet, which is nominallyinclined at a nominal inclination angle relative to a first of the twosurfaces. Such a sample, a sample 90, is depicted in FIG. 9 , accordingto some embodiments. Sample 90 includes an external, flat first surface92 a, and external, flat second surface 92 b, and an internal facet 94.Internal facet 94 is nominally inclined at a nominal inclination angle ωrelative to first surface 92 a. Sample 90 is shown being inspected bysystem 900.

System 900 includes an ICA 904 and a LFC 922, which may correspond tospecific embodiments of ICA 104 and LFC 122, respectively. ICA 904 mayinclude a light source, at least one sensor, and, optionally, opticalequipment (all not shown), which may correspond to specific embodimentsof light source 112, at least one sensor 114, and optical equipment 118,respectively. System 900 may further include a controller, an orientablestage, and a computational module (all not shown), which may correspondto specific embodiments of controller 108, first stage 142, andcomputational module 130. The controller may be functionally associatedwith ICA 904 components, the stage, and the computational module in asimilar manner to controller 108 functional association with ICA 104components, first stage 142, and computational module 130, respectively.

In operation, ICA 904 generates a pair of incident LBs: a first incidentLB 905 a and a second incident LB 905 b, which is parallel to firstincident LB 905 a. First incident LB 905 a is projected nominallynormally to first surface 92 a. A first returned LB 933 a is obtained byreflection of first incident LB 905 a off first surface 92 a and issensed by a sensor (not shown) of ICA 904.

Second incident LB 905 b is folded by LFC 922, as indicated by a foldedLB 913 b. Folded LB 913 b impinges on second surface 92 b. A transmittedLB 917 b indicates a portion of folded LB 913 b, which is transmittedinto sample 90. Transmitted LB 917 b nominally normally impinges oninternal facet 94. That is, a nominal folding angle of LFC 922 and anorientation of sample 90 relative to LFC 922 are selected such thattransmitted LB 917 b will nominally normally impinge on internal facet94.

A reflected LB 921 b indicates a portion of transmitted LB 917 b, whichis specularly reflected off internal facet 94. An emerged LB 925 bindicates a portion of reflected LB 921 b, which exits sample 90 byrefraction via second surface 92 b. Second returned LB 933 b is obtainedby the folding of emerged LB 925 b by LFC 922. Second returned LB 933 bis sensed by the sensor of ICA 904.

According to some embodiments, the angular deviation of second returnedLB 933 b relative to first returned LB 933 a may be obtained from thehorizontal distance between a second spot and a first spot formed bysecond returned LB 933 b and first returned LB 933 a, respectively, onthe photosensitive surface of the sensor, as described above in thedescriptions of system 100 and method 700. From the measured value ofthe angular deviation, a deviation in the (actual) inclination ofinternal facet 94 from the nominal inclination thereof may be derived,essentially as described in the descriptions of system 100 and method700.

FIG. 10 schematically depicts an optical-based system 1100 for internalfacet metrology of samples, according to some embodiments, System 1100is configured for use with samples including an external and flatsurface and an internal facet, which is nominally inclined at a nominalinclination angle relative to the surface. Such a sample, a sample 1010,is depicted in FIG. 10 , according to some embodiments. Sample 1010includes an external, flat (first) surface 1012 a and an internal facet1014. Internal facet 1014 is nominally inclined at a nominal inclinationangle ω′ relative to first surface 1012 a. Sample 1010 is shown beinginspected by system 1100.

System 1100 includes an ICA 1104 and a LFC 1122, which may be similar toICA 104 and LFC 122, respectively, but differ therefrom as describedbelow. ICA 1104 may include a light source, at least one sensor, and,optionally, optical equipment (all not shown), which may be similar tolight source 112, at least one sensor 114, and optical equipment 118,respectively. System 1100 may further include a controller and acomputational module (all not shown), which may correspond to specificembodiments of controller 108 and computational module 130. Thecontroller may be functionally associated with ICA 1104 components andthe computational module in a similar manner to controller 108functional association with ICA 104 components and computational module130, respectively. System 1100 may further include an orientable stage(not shown), which may be similar to first stage 142, and which may becontrolled by the controller.

In operation, ICA 1104 generates a pair of incident LBs: a firstincident LB 1105 a and a second incident LB 1105 b, which is parallel tofirst incident LB 1105 a. First incident LB 1105 a is projectednominally normally to first surface 1012 a. A first returned LB 1133 ais obtained by reflection of first incident LB 1105 a off first surface1012 a and is sensed by a sensor (not shown) of ICA 1104.

Second incident LB 1105 b is folded by LFC 1122, as indicated by afolded LB 1113 b. Folded LB 1113 b impinges on first surface 1012 a. Atransmitted LB 1117 b indicates a portion of folded LB 1113 b, which isrefracted into sample 1000. Transmitted LB 1117 b nominally normallyimpinges on internal facet 1014. That is, a nominal folding angle of LFC1122 and an orientation of sample 1000 relative to LFC 1122 are selectedsuch that transmitted LB 1117 b will nominally normally impinge oninternal facet 1014.

A reflected LB 1121 b indicates a portion of transmitted LB 1117 b,which is specularly reflected off internal facet 1014. An emerged LB1125 b indicates a portion of reflected LB 1121 b, which exits sample1000 by refraction via first surface 1012 a. Second returned LB 1133 bis obtained by the folding of emerged LB 1125 b by LFC 1122. Secondreturned LB 1133 b is sensed by the sensor of ICA 1104.

According to some embodiments, the angular deviation of second returnedLB 1133 b relative to first returned LB 1133 a may be obtained from thehorizontal distance between a second spot and a first spot formed bysecond returned LB 1133 b and first returned LB 1133 a, respectively, onthe photosensitive surface of the sensor, as described above in thedescriptions of system 100 and method 700. From the measured value ofthe angular deviation, a deviation in the (actual) inclination ofinternal facet 1014 from the nominal inclination thereof may be derived,in a similar manner to the derivation of the actual inclination angle α′from the angular deviation δ (described above in the description ofsystem 100 and method 700).

According to some embodiments, the nominal folding angle of LFC 1122 maybe selected such that an intensity of second returned LB 1133 b ismaximized.

It is appreciated that certain features of the disclosure, which are,for clarity, described in the context of separate embodiments, may alsobe provided in combination in a single embodiment. Conversely, variousfeatures of the disclosure, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the disclosure. No feature described in the context of anembodiment is to be considered an essential feature of that embodiment,unless explicitly specified as such.

Although stages of methods according to some embodiments may bedescribed in a specific sequence, methods of the disclosure may includesome or all of the described stages carried out and/or occurring in adifferent order. A method of the disclosure may include a few of thestages described or all of the stages described. No particular stage ina disclosed method is to be considered an essential stage of thatmethod, unless explicitly specified as such.

Although the disclosure is described in conjunction with specificembodiments thereof, it is evident that numerous alternatives,modifications, and variations that are apparent to those skilled in theart may exist. Accordingly, the disclosure embraces all suchalternatives, modifications, and variations that fall within the scopeof the appended claims. It is to be understood that the disclosure isnot necessarily limited in its application to the details ofconstruction and the arrangement of the components and/or methods setforth herein. Other embodiments may be practiced, and an embodiment maybe carried out in various ways.

The phraseology and terminology employed herein are for descriptivepurpose and should not be regarded as limiting. Citation oridentification of any reference in this application shall not beconstrued as an admission that such reference is available as prior artto the disclosure. Section headings are used herein to easeunderstanding of the specification and should not be construed asnecessarily limiting.

What is claimed is:
 1. An optical-based method for validating anorientation of one or more internal facets of a sample relative to anexternal, flat surface thereof, the method comprising: providing asample comprising an external, flat first surface and an internal facetnominally inclined at a nominal inclination angle p relative to thefirst surface; providing a light guiding arrangement (LGA) configured toredirect light, which is incident on the LGA in a directionperpendicular to the first surface, into or onto the sample, such thatlight, transmitted thereby into the sample, impinges on the internalfacet nominally normally to the internal facet; generating a firstincident light beam (LB), directed at the first surface normallythereto, and a second incident LB, parallel to the first incident LB anddirected at the LGA; obtaining a first returned LB by reflection of thefirst incident LB off the first surface; obtaining a second returned LBby redirection by the LGA of the second incident LB into or onto thesample, reflection thereof off the internal facet, and inverseredirection by the LGA; measuring a first angular deviation of thesecond returned LB relative to the first returned LB; and deducing anactual inclination angle p′ of the internal facet relative to the firstsurface, based at least on the measured first angular deviation.
 2. Theoptical-based method of claim 1, wherein the sample comprises a firstpart and a second part, between which the internal facet extends,wherein the first part is positioned between an external second surfaceof the sample and the internal facet, and wherein a transmitted LB,constituting a portion of the second incident LB, which is directly orindirectly transmitted into the sample, enters into the sample via thesecond surface.
 3. The optical-based method of claim 2, wherein the LGAcomprises a light folding component (LFC) nominally configured to foldlight, at least when projected thereon in a direction perpendicular tothe first surface, at a light folding angle equal to the nominalinclination angle.
 4. The optical-based method of claim 3, wherein theLFC is or comprises a prism, one or more mirrors, and/or a diffractiongrating.
 5. The optical-based method of claim 4, wherein the lightfolding angle is insensitive to variations in a pitch of the LFC.
 6. Theoptical-based method of claim 5, wherein the LFC is or comprises apentaprism or a like-function prism, or a pair of mirrors set at anangle relative to one another, or a like-function mirror arrangement. 7.The optical-based method of claim 3, wherein the LGA further comprises acoupling infrastructure configured to guide the light, folded by LFC,onto or into to the sample, such that light, transmitted thereby intothe sample, nominally normally impinges on the internal facet.
 8. Theoptical-based method of claim 7, wherein the coupling infrastructurecomprises a coupling prism (CP), comprising an external, flat CP firstsurface, an external, flat CP second surface, nominally inclined at thenominal angle relative to the CP first surface, and an external CP thirdsurface, opposite the CP second surface; wherein the CP has a samerefractive index as the first part of the sample or a refractive indexclose thereto; and wherein the CP is disposed such that the CP firstsurface is parallel to the first surface of the sample, and is furtheroriented such that the light, folded by the LFC, nominally normallyimpinges on the CP second surface.
 9. The optical-based method of claim8, wherein the coupling infrastructure further comprises ashape-compliant interface, which is disposed between the CP thirdsurface and the sample and has been made to assume a shape such that theCP first surface is parallel to the first surface of the sample.
 10. Theoptical-based method of claim 9, wherein the shape-compliant interfacehas a same refractive index as the first part of the sample or arefractive index close thereto.
 11. The optical-based method of claim 9,wherein the shape-compliant interface is or comprises a liquid and/or agel.
 12. The optical-based method of claim 2, wherein the sample is aprism, a waveguide, or a beam splitter.
 13. The optical-based method ofclaim 8, further comprising an initial calibration stage wherein a goldstandard sample is utilized to calibrate orientations of the LFC, theCP, and/or the sample. The optical-based method of claim 8 methodfurther comprising generating an additional incident LB, which isdirected at the CP first surface and in parallel to the first incidentLB, and, wherein, an orientation of the CP is (a) calibrated and/or (b)tested for correct orientation during the measurement of the firstangular deviation, by measuring an additional angular deviation of anadditional returned LB relative to the first returned LB, the additionalreturned LB being obtained by reflection of the additional incident LBoff the first CP surface.
 14. The optical-based method of claim 1,wherein the first angular deviation is obtained from measuredcoordinates of a first spot and a second spot formed by the firstreturned LB and the second returned LB, respectively, on aphotosensitive surface of a light or image sensor. The optical-basedmethod of claim 1, wherein the first angular deviation is measured usingan autocollimator.
 15. The optical-based method of claim 8, comprisingthe CP, and wherein the actual inclination angle of the internal facetrelative to the first surface is obtained from the measured firstangular deviation taking into account the values of the actualinclination angle of the CP second surface relative to the CP firstsurface, and the refractive index of the first part of the sample, and,optionally, the actual light folding angle of the LFC.
 16. Theoptical-based method of claim 1, wherein the sample comprises k>1additional internal facets nominally parallel to the internal facet;wherein in the obtaining of the second returned LB, k additionalreturned LBs are obtained by reflection of k LBs off of each of the kadditional internals facets, respectively, the k LBs jointlyconstituting a portion of the second incident LB, transmitted into thesample and further transmitted via the internal facet; wherein in themeasuring of the first angular deviation, k additional angulardeviations of the k additional returned LBs relative to the firstreturned LB are measured; and wherein in deducing the actual inclinationangle p′ of the internal facet, (i) k additional actual inclinationangles of each of the k additional internal facets are additionallydeduced, and/or (zz) an average actual inclination angle equal to, orabout equal to, an average over the actual inclination angles of theinternal facet and the k additional internal facets, is deduced, theaverage actual inclination angle being indicative of the actualinclination angle p′ of the internal facet.
 17. The optical-based methodof claim 16, wherein k>2, wherein a first of the additional internalfacets is positioned between the internal facet and a second of theadditional internal facets, and wherein, for each m such that 2<m<k−1,an zzr-th of the k additional internal facets is positioned between an(m−1)-th and an (m+1)-th of the k additional internal facets.
 18. Theoptical-based method of claim 16, wherein each of the internal facet andthe k additional internal facets is configured to reflect light at arespective spectrum, each spectrum being distinct from the otherspectra, so as to allow distinguishing between each of the secondreturned LB and the k additional returned LBs
 19. The optical-basedmethod of claim 2, wherein the sample comprises k>1 additional internalfacets nominally parallel to the internal facet; wherein in theobtaining of the second returned LB, k additional returned LBs areobtained by reflection of k LBs off of each of the k additionalinternals facets, respectively, the k LBs jointly constituting a portionof the second incident LB, transmitted into the sample and furthertransmitted via the internal facet; wherein in the measuring of thefirst angular deviation, k additional angular deviations of the kadditional returned LBs relative to the first returned LB are measured;and wherein in deducing the actual inclination angle p′ of the internalfacet, (i) k additional actual inclination angles of each of the kadditional internal facets are additionally deduced, and/or (zz) anaverage actual inclination angle equal to, or about equal to, an averageover the actual inclination angles of the internal facet and the kadditional internal facets, is deduced, the average actual inclinationangle being indicative of the actual inclination angle p′ of theinternal facet.
 20. The optical-based method of claim 3, wherein thesample comprises k>1 additional internal facets nominally parallel tothe internal facet; wherein in the obtaining of the second returned LB,k additional returned LBs are obtained by reflection of k LBs off ofeach of the k additional internals facets, respectively, the k LBsjointly constituting a portion of the second incident LB, transmittedinto the sample and further transmitted via the internal facet; whereinin the measuring of the first angular deviation, k additional angulardeviations of the k additional returned LBs relative to the firstreturned LB are measured; and wherein in deducing the actual inclinationangle p′ of the internal facet, (i) k additional actual inclinationangles of each of the k additional internal facets are additionallydeduced, and/or (zz) an average actual inclination angle equal to, orabout equal to, an average over the actual inclination angles of theinternal facet and the k additional internal facets, is deduced, theaverage actual inclination angle being indicative of the actualinclination angle p′ of the internal facet.